
It's faar far from medieval renaissance. The style of the dresses are more late/middle-ish 19th century. I know its hard to determine the exact time it sets because the author just mixes up a bunch of random style, but i think it must be some alternate 1850-90s setting. (Btw feudalic peasantry was this heavily a thing in the 1920s(!) At least in my country, and i live in Europe mind you)
Lets assume it takes place in their capital city so under "commoner" they probably mean citizen/civilian. They are not nobles nor peasants, they can be still pretty rich too. So the butique was probably aimed at low and middle class civilians (the dresses are too plain for a more well of commoner lady, so it would be appropriate for a lower class one)
Your everyday maid likely had 1 or 2 sets of outfits(plus her work clothes). They wore lots of layers so the more valuable outer layer was protected from the sweat/oils from the skin. They had more undergarments and washed them frequently.
Peasants made their own clothes (and their fabric too)
(Sorry i dont want to sound preachy, i just got really into it and it became quite long)
Im not sure the author grasps the "commoner" concept quite yet tho... cos that seemed pretty high end to me, specially for a medieval/renaissance-ish looking world