It is true that the potter's angel can be a bit of a challenge. They are beautiful animals, and can make a nice addition to a display. I highly recomend that before you buy one that you ask the worker ar your LPS to feed it (preferably the foods that you are considering feeding it, or at least some frozen algae foods (Ocean Nutrition's Formula 2). If the angel eats it ravenously then it is a good buy, and if it doesn't seem interested then either pass it by or give it another week and have them feed it again (if a fish is brand new in the store it may be to stressed out or frightened to eat). A good pet store will be more than happy to show you that a fish is eating, and if they say that they can't then I would suggest finding a different store, because they are most likely hiding something (let the pet store manager know that you won't buy anything there, and why. Maybe they will get the hint and change.).
Also check the fish over very carefully. Angels are prone to tremetode infestations, Oodinium, and Uronema infestations. Make sure the body is full and the colors are crisp. An angel with Oodinium, or Uronema will have a hazey, paled look. Check the eyes, they should be crystal clear. Flukes (tremetodes) can appear as cloudiness on the eye, and an off colored, ruffed up splotch on the flanks just behind the pectoral fins.
Most important... quarentine your new fish for a couple of weeks. Treat them with a 17% formaldahyde solution (Formalin brand), and with copper (.15 to .20 ppm concentration). If you give the new fish a freshwater bath for 5 minutes before introducing it to the display tank you will kill off any external flukes they may have. Another medication that I have found to work on the dreaded Monogenetic trem
atode is "Fluke Tab".
Since I started working in a petstore as the Saltwater manager I have seen well close to a hundred potter's angels and I have been able to get about 85% of them to eat frozen and dried foods. The rest of them were just to darn picky.
Give them a try, but be choosey.