Same thing happened to me, but I didnt need to step foot into a store.
Called around and a store happened to have two iPhones that I wanted. After saying I would be in and take it SA said "cool".
Within 5 minutes I was called back and I was told I needed to purchase screen protector, a case, and Applecare. When I declined saying I may decide on Applecare on another date and I didnt want to purchase a case sight unseen the SA said ok. Then another 5 minutes later SA called again to apologize that the phones I was to purchase were actually for someone else. Sorry about the confusion <click>.
I thought it was just an isolated event with a shifty SA but it sounds like its common practice at RadioShack. Hopefully Apple stops supplying RadioShack soon.