Actually, watching the LFS feed the tank that has the fish in it that I want is my favorite part about going to the LFS. I have them feed just about everything I can think of to the tank and watch the fish I want. I watch to see what it eats, what it doesnt eat, and how aggressive it is towards eating with other tankmates.
Watching the PFF eat at the LFS was a great experience. I had them toss in mysis and it ate that. I had them toss in some pellets and it tried it, but didnt eat it. I had them toss in some worms, and it stayed clear of that. I had them toss in some brine and everything ate everything. I then asked them about the emerald entre and the LFS said that they didnt have any available to them and that it probably wouldnt eat it anyways.
Tangs, hmmmmm. 2 tangs in a 75 gallon tank. Honestly, I do not know if it is enough room.