The answer to your question really depends on what era of the Roman Republic/Empire you are talking about. The crisis of the 3rd century in the Roman Empire led to tighter imperial restrictions on jobs deemed important by the state and the urban centers of the Empire. Many collegia "guilds" (but a better analogy would be trade association or union)* were, therefore, controlled by imperial administrators to ensure that they provided the necessary provisions for the Empire.

So how were these collegia controlled? Besides forcing the collegia to have a maximum price on their goods (as evidenced by Diocletian's Edict on Maximum Prices), many occupations became hereditary by the time of Constantine.

These new changes raised taxes and forced a heavy burden on some people, namely the decurions (town councillors) who basically had to pay the difference if their town was unable to raise the funds for these taxes. Thus, many decurions attempted to flee to the military to avoid doing their duty (and later the church). Not wanting to lose these officials, laws were created to prevent such escape. The Theodosian Code notes, "Since some men desert the municipal councils and flee for refuge to the protection of the military service, we command that all persons who are found to be not yet under the authority of the chief centurion shall be discharged from the military service and shall be returned to the same municipal council" (Theodosian Code XII.I).

Others jobs like being a shipmaster (Theodosian Code XIII.v) and being a breadmaker (Theodosian Code XIII.v) also became heriditary, and one could not enter the profession unless they had inherited the hereditary right even if backed by the necessary guild.

Finally, the Empire also saw the rise of coloni (tenant farmers), who were forced live around the villages due to a lack of jobs in the cities. In order to deal with the crisis of agriculture during the third and fourth centuries, the Empire under Constantine required tenant farmers to stay put. The Theodosian code notes, "Any person whatsoever in whose posssession a colonus belonging to another is found not only shall restore the said colonus to his place of origin but shall also assume the capitation tax on him for the time" (Theodosian Code V.xvii). It became essential for these farmers to stay where they were to ensure a steady grain supply. Thus, these tenants became tied to the land and were unable to work as anything but farmers due to these policies.

Sources all from: Lewis, Naphtali, and Meyer Reinhold. Roman Civilization: Selected Readings. 3rd ed. Vol. 2. 2 vols. New York: Columbia University Press, 1990.

Edit: *Thanks for /u/blueb0g for pointing out my oversimplification of the concept of Collegia. Collegia at their core were social clubs that could be full of members of the same occupation. And though Collegia is translated as guild, and can be loosely seen as a trade association, it is important to note that most would be more reminiscent of today's country clubs, rather than a full union.

The Roman world of the Republic and the Principate did not know such a thing as a standardized wage, or even regular wages at all. Indeed, for most Roman laborers the idea of permanent employment appears to have been conceptually non-existent. Most Roman laborers in the city were unskilled, unlanded workers, who mainly subsisted on daily wages gotten through day labor, the uncertainties of which were as apparent then as now. This likewise appears true of the country, although tracking free, unlanded labor is extremely difficult there, and we do not adequately understand how unlanded labor could have moved around, except to a certain extent around the ager Romanus, where it appears that seasonal migratory work could be found between suburban fields and urban employment. Likewise, we have evidence (e.g. Suetonius, Vesp., 1) that bodies of rural workers moved between entire districts of Italy in fairly large numbers, chasing the differing agricultural seasons of different regions and crops. But whatever the specifics, it is generally acknowledged that most Roman laborers were probably unskilled, unlanded, and semi-itinerant, even within the city, though the degree to which a "permanent" urban population existed is heavily debated.

Shopkeepers and skilled workers (artisans and so forth), categories that generally overlap significantly (an artisan likely owns his own shop), are the major exceptions. These workers were skilled and economically valuable for more than their human labor. However, while we know significantly more about them our information is still horribly limited. Most of our evidence for skilled workers in the city is epigraphic, but this presents massive problems. For example, Brunt mentions that of all goldsmiths in the city known at that time from epigraphy only 7% are of free birth. Of the remainder, some 58% are freedmen and the rest are slaves. There are problems here. First of all, the identification of freedmen and slaves via nomenclature is increasingly becoming highly contested. Onomastic evidence is often insufficient without (often present) additional markers of status, like mention of former owners and so forth. Second, it is a well known problem that freedmen are vastly over-represented in epigraphy, and they seem to be precisely those most likely to take advantage of the so-called "Epigraphic Habit." So these numbers may be representative or they may not be. This is typical of the source criticism that must be done for these sorts of workers. Additionally, of skilled workers that we know of from textual evidence the presence of freedmen and slaves appears unusually pronounced. Freedmen shopkeepers made up the administration of Augustan vici, which would suggest that shopkeepers--those parts of urban society most likely to be permanent residents, and recognized as such under Augustus by their formal association with local adminstration--were in fact primarily freedmen, or at least that for some reason free shopkeepers were being excluded. Likewise, skilled workers are often spoken of in association with slaves in our texts. Treggiari has very convincingly pointed out that this appears to be something of an elite literary habit: shopkeepers are below the dignity of senators (who are not legally allowed to own shops themselves, though they can have slaves do it for them through their peculia), and therefore in the senatorial imagination of oratory they are the same thing. However, there do seem to be indications that servile workers were common in the workshops of skilled workers. I've mentioned the peculia thing (we know of many slaves "owning" shops of their own) and Brunt points out that slaves are the most likely to become skilled workers, since typically they would be taught some sort of trade or be bought for that exact purpose. Upon manumission they would enter the free workforce with those same skills intact. This idea, though to a great degree speculative, has been quite influential. Meier, for example, conjectured a "plebs contionalis" made up of fairly affluent shopkeepers near the forum who could afford to attend contiones on a regular basis because they could leave their shops to their slaves, and Tatum (in my opinion totally against the evidence) argued that this group made up the majority of Clodius' armed violence. Contrarily, Mouritsen argues (I think also incorrectly) that actually shopkeepers could not afford to attend contiones, though he gives no evidence except to refer somewhat vaguely to our little information about unskilled laborers, which tells us nothing about skilled workers.

This is all to give a very brief look into only a few of the problems that we face in trying to say anything at all about the people you're asking about in the Republic and the Principate. We know, frankly, practically nothing about skilled workers for sure, and even less about unskilled labor. We have very little information about how shops were organized (though family shops with servile and freedman workers seems probably common, although I'm not actually sure that the epigraphic evidence for sons in the same profession as their fathers is actually very good at all), we have very little information even about how common they were, our changing understanding of collegia has called very much into question how they got along with each other (there appears now to be basically no basis for the assertion that collegia had any real economic role whatsoever), we do not know what sort of labor they typically used or where they got it, we do not know how much they paid that labor (if at all), etc. We're not even sure where these people are economically. Yakobson pointed out that the property requirement in the comitia centuriata for the equites (HS 400k under Augustus by Lily Ross Taylor's estimate, which is generally accepted) is, by the most conservative estimates, fully ten times as great as the level necessary to enter the first property class (HS 40k-50k, though other estimates like Nicolet's push it even lower, further widening the gap). Yakobson notes that this gap appears to have been much larger than for the other classes (for whom we have less information), and that somewhat paradoxically the wealthiest property class also would likely have had the greatest variation in wealth between centuries. Does this mean that we should actually place shopkeepers not in the lower voting classes, but actually in the first and second class? Yakobson thinks so, at least for a significant number of more successful skilled workers--others are not so sure.