The story sounds odd; if that happened in our shop I'd show the customer the damaged pedal and explain/show how the retaining nut had stripped, or the axle end had cracked, or whatever caused the failure. I doubt he's doing this on purpose to sell you a pedal set, wrenches don't make commission on parts sold, and even if he's the owner (doubt that) he's not going to make much on replacement pedals.
Do you have the broken pedal and can you post a pic of the part of it that failed? Did the pedal axle stay in the crankarm? From your description it sounds like the retaining nut backed itself off, but depending on the pedal type that may/may not be something that can be fixed. An option is to hit a local bike co-op. Look for the grumpy guy with a beard and suspenders. Show him the pedal and he'll probably have just the part you need in his recycle bins.
Best of luck with all your med issues, most of us have been there in one form or another. I still get shoulder pain from a bike v. pickup incident 15 years ago.