I've had one for about 2 months now. He was eating flake food at the lfs, but I switched over to live black worms, mysis, and brine shrimp while in the qt and he took to those right away, especially the worms. He has been in the dt for a month now and is eating like a pig.
The key is to make sure it's eating at the lfs, is alert and actively exploring the tank. If you can get black worms that helps because they'll get a feeding response out of a finicky eaters.