Whenever I go to a printshop I try to give them the most suitable and high quality print-ready files, so that they do not need to take any extra steps or adjust things on the way (although they sometimes need).
On the other hand, someone that is not a designer/artist may not know how to give the best setup and printshops would need to tweak things in order to fit their printer needs.
Then a question comes to my mind:
Do printshops actually charge more to non-designer customers due to that extra work?
Makes sense as time is money, but, is this actually true?
I have had non-designer friends who paid more for simillar things that I did for much less money.