Did you happen to pay by check? If so you must wait a week before RadioShack will issue you a refund (unless you opt to have a check mailed to you by corporate). This would make sense as to why one of the associates you talked to said to come back next week...
If you did pay with cash, did you try going back to the store in the afternoon? Surely they would have enough cash by then to do a return. There is nothing that I hate more then the first customer of the day walk in with a $100+ return who paid with CASH and wants CASH!
And lastly like others have posted, just ask for the DM's phone number, and call him on your cell phone (or better yet ask to use their phone) and call him/her while in the store..
Oh, and yes RS employees do work on commission (but don't think they are making much off your sale, cause they aren't) And really the only people who would try to prevent you from returning it is the original sales guy and maybe the manager from that store. No other associate cares if someone else gets a return. They only care about trying to sell something, and hoping that maybe YOU will buy something from THEM after they return your scanner..
OK, one last thing, I promise, which scanner was it ? Was it an old disco/deval scanner? The other managers might not want to get stuck with an old/ugly/beat up piece of junk. Once a store has something (like a scanner) returned, it's stuck there until someone buys it in the condition it is returned in. So if it has no box, then it is going to be hard to sell to someone else without a box.
OK, I hope this sheds some light into the thinking of RS.