More can always be said from anyone who knows about the matter, so don't let my linking stop you from writing up - we always welcome more answers! For the meantime, OP, on the matter of guilds, you may be interested in this previous post from u/CowboyLaw, where they also link to several of their previous guild-related answers.

Thanks to /u/DanKensington for summoning me to this question! The most applicable of my previous answers is this one. And, the short answer is, trade guilds (which is all I can speak to) weren't specifically interested in whether you were "cheating" your customer. They WERE interested in quality control, such that you wouldn't build a cheap wall that would fall down and crush someone and thereby bring disrepute on the local masons guild. But if you had promised Lord Wallwanter that you'd build the wall out of limestone, and it was clearly granite, they wouldn't necessarily care. Now, guilds DID hear and quasi-adjudicate complains against their members. So, if Lord Wallwanter realized he'd gotten the wrong rock, and if he brought his complaint to the Guild, they'd act on it. Investigate, etc. But usually the most the Guild could do was throw you out of the guild. (I say usually only because I don't know the bylaws of every trade guild in every country over many centuries, so perhaps some of them had a charter where members agreed to be fined by the Guild under certain circumstances, so maybe that happened, but it would be very rare.) And, to be very clear, the Guild would NOT care whether Lord Wallwanter was or wasn't cheated. They'd care whether your actions would bring disrepute on the guild itself. So their disciplinary actions were solely intended to protect their own interests.

The other questions are well addressed by my previous comments. Hope this helps, and let me know if you need any additional information.