I have kept Idols on 2 occasions. I was successful getting them to eat nori that was been treated with garlic. I can't remember the brand, but it was not cheap. Both of mine also ate spectrum pellets. PE mysis with selcon works too.
You may need to dump a lot of food in the tank if you have other fish that are competitive for food. However, once they start eating, they are fine.
When you see them for sale, have them feed them. If the fish does not look at all interested, I would pass until you find one that at least tried to eat. I they taste the food and spit it out, you have a chance at getting them to eat. I got both of mine from Tongs.