Pixie passed way !

[monster]

Look for a frog that looks alert and doesn't have shed or anything stuck to him. I would ask to hold the frog, if it doesn't try to get away from you and just sits there that could be a sign theres something wrong. If the frog is just sitting in the water bowl I would ask if this is normal for the frog also, if it sits in the bowl all the time this would also be a indicator that it is sick. I would ask them to feed the frog for you to see how he reacts to the food, again if it doesn't at least catch his attention I wouldn't purchase it, when these frogs are babies they have one thing on there mind and that is food. I would also ask were they purchase the frogs from and do some googling to see if you can get any feed back on the seller/breeder.
The crickets were pretty big for the frog but I don't think that is what made him pass, if he was pooping them he was digesting them and you were giving days off inbetween feedings. Generally the rule with feeders is no thicker then the distance between his eyes and no longer then half the body length, this is really good to follow when they are babies and juveniles to be safe. Usually when they are adults they can handle something a little bigger, people feed fuzzies and they can take them no problem.
For the uvb it wont hurt them but it isn't needed, these frogs are adjusted to calcium metabolism with out uvb and in the wild when the sun comes out they pretty much burrow down or sit under leaves etc. and this what the vitamins are for. A good vitamin to get is Repashy calcium plus, it has all the vitamins you need in one. But again Uvb will not kill them and could have some benefits.