All the historical documentation - and images - surrounding the time of Haydn - Mozart - Beethoven suggest that when their works were premiered, it was upper or upper middle class people who attended the concerts.
So what was everyone else listening to? What was the popular music amongst the peasants and working class of this period and how would they hear it?
First, it is easy to get mislead by the compositions you normally hear now, by Mozart, Haydn, Beethoven: usually they're the big works, symphonies, operas, concertos. But these three composers also wrote many small things that you don't hear nearly as often (how many times have you heard one of the three duets Beethoven wrote for clarinet and bassoon?). A lot of music was made by people themselves, often small ensembles, mostly amateurs, who would buy published sheet music. So, simply because elites tended to go to grand concerts does not mean these composers did not reach people lower down. And there were quite a few other composers , not so famous, who would also meet this demand- Benda, C.P.E. Bach..
If you want to get an idea of what the shepherd would be playing to his sheep, on bagpipes, there is a problem: the shepherd wasn't writing it down. However, it's possible to get some ideas of it, because there were plenty of itinerant musicians who were heard and loved, and someone would often write down what they were playing because they wanted to play it themselves. The amateur musicians who could read would often transcribe useful pieces into manuscript books, and a number of these have survived. These are , not surprisingly, pretty regional in their repertoire. A manuscript of 1738, of a William Dixon, that has a lot of tunes with complex variations, has shown there was a very impressive level of bagpipe playing in the north of England, and that continued into the 19th c. with players like John Peacock. The tunes often have rude names ( Hit Her Between the Legs) but they're anything but simple. And they have a lot of 3/2 hornpipes- a dance form which was typical for the north of England but which is now lost. A pretty good example would be Bridghe Chaimbeul playing Hackey Honey here, ( starting at 0:54).
The Dixon MS has just pipe tunes, but many of these music books have a mix, for fiddles or other instruments. Some have regional dance tunes, like the Dixon MS, but also popular songs, show tunes for the musical theater of the time by songwriters like Charles Dibden ( a favorite of sailors) or Leonard McNally, like The Lass of Richmond Hill. Some have hymns. Some have mostly hymns.
To pick a completely different location, circa 1786 the Van Pelt family of musicians in the Flemish town of Tongeren began to keep a book of tunes for fiddle, that they found useful. Like the English books, it's a mix, but different. Instead of hornpipes, there are quarrées, square dances, in 6/8 ( you can hear a quarrée , typically frivolous, in the scherzo in Beethoven's 9th Symphony). Instead of show tunes from Covent Garden, there are songs from the French theater, like Nicodeme dans la Lune. And while there's none of the complex theme-and-variation of the Dixon MS and other northern English books, there's a lot more chromatic complexity....which might explain why there are also some scales, for practice.
Schreurs, E. (1996). Late 18th- and Early 19th-Century Polyphonic Settings of Speelman Music from Maastricht. Revue Belge De Musicologie / Belgisch Tijdschrift Voor Muziekwetenschap, 50, 153-165. doi:10.2307/3687042