Howdy,
I guess I am against popular opinion: I wouldn't do it. Not necessarily out of etiquette, but out of respect for the fish: You said you frequent LFSs across the state. Traiding fish from one store to the other means for the fish: bagging, road trip, different water chemistry. I know that this happens often enough on the fish's trip from origin to home aquarium, but it's one more trip nevertheless.
And, as others said, there is always the risk of purchasing the fish for trade-in and getting stuck with them because the other store won't take them...
HarleyK
