I believe it's not that they are hard to keep, but they don't ship well and stress very easily.
You need to have a well established tank with lots of liverock and pods for them to forage on as they are very active hunters. You must have a sand bed for them as they bury at night to sleep, and you need to be able to feed them often.
Buying from Divers Den is by far your best bet in getting a very healthy fish.