then it would be easy to go to a real optician and get a prescription, and compare that one with the one you get from the shop.
The optician also can check if the lenses you get are what was on the prescription.
I have been once in such a shop, and all they did was check with the computer, so I walked out right away.
When I order new glasses, they first do with the computer, because that just gives them a direction where to start with the manual check