I sell lots of frogs and deal with import and CB red eye tree frogs. Out of the 45 or so import red eye tree frogs I have been through this year I have had no problems. I quarentine them for a period of 2 weeks to a month before selling them. I have kept several for myself and have had no problems from them. Yes there are some crappy imports out there for sale.
You have to deal with a reputable dealer who hopefully has a good importer. Also as with any animal no matter where it comes from it should be quarentined for a period of no less than a month before introducing it to an established group.
Also look at what you pay for the frog. If you are paying less than $40 for an adult frog, I would question it seriously. This means either the seller didn't pay much for them, they haven't had them long, or they have a large amount of them to get rid of. All of these factors can affect the condition of the frog. It might be cheaper to order it online froma large retailer, but the smaller individuals like myself put time and effort into their animals. I feed vitamins, clena the cages regularly, and inspect each of my animals every day to check for problems. If there is any doubts I will not sell the animal.
Basically you get what you pay for. If the dealer is a good one they will work to resolve any problems. Also examine how you have set them up. red eye require near perfect conditions and do not tolerate a dirty terrarium.