Purchasing a new Tokay Gecko...
Chances are if you're purchasing a new tokay gecko, it's going to be wild caught. Here are some things you'll need to keep in mind when selecting one.
1) If it's a wild caught tokay, freshly imported, it'll probably be very skinny and teaming with parasites. I recommend a vet visit with a fresh fecal sample to see what it needs to be wormed for. That way the proper worming medication can be administered to treat the problem. The way any of my animals have been wormed has been- one initial dose, then a repeat dose in two weeks. My understanding is that the first dose kills off the existing parasites and the second dose kills off the parasites that were only eggs when the first dose was administered. I don't think the medication will kill the eggs which is why the second dose is needed. Also during this time you need to keep the cage immaculate, removing any fecal matter from the cage as soon as possible to prevent the gecko from coming in contact with the feces and reinfecting itself. I suggest setting up a quarantine cage with the bare necessities, even if you don't plan to house it with another tokay later. By doing this it'll be easier to keep clean during the two week worming period. It'll be easy to see if the gecko is eating since the prey items can't hide, as well as keep an eye out for any changes in the feces. When I set up quarantine cages, I use a glass aquarium with a screen top (everything can be disinfected) and paper towels for substrate. I put in an empty tissue box and a paper towel roll for hiding places. This is just during the quarantine period which is at least 30 days. You don't want to put a new tokay in with your established group/tokay until you are sure it is healthy and free of parasites. Also, by adding a tokay to a cage with another tokay/other tokays with already established territories, you could be asking for problems. I would in that case, set up another cage and introduce the whole group at one time. Make sure there is only one male per cage and keep an eye out for any aggression, such as bite marks and posturing (the females can get quite nasty too).
2) You're going to want to make sure it's alert. It'll probably be rather aggressive if it's in decent shape (unless it's a tame captive bred tokay).
3) The eyes should not be sunken in.
4) Fecal matter should not be crusted around the vent. A gecko like that is probably ill.
5) Check for any lumps on the skin. Often small bumps are parasites under the skin or they can be abcesses, tumors, or cysts.
If you are a sucker like me, and feel the need to rescue one of these poor geckos (as I've done with many a lizard), you'll need to find a good vet that treats exotics. ARAV is a good place to check or you can check out Melissa Kaplan's site to find a vet in your area.