There are certainly plenty of cases of WC animals coming into the country in bad shape, eaten up with parasites, imported by people who don't really know how to care for them properly or acclimate them, and then they get sold to the poor buyer who promptly feels like he killed them. There's not much you can do about all the stuff before they hit your hands, but once you get them just remember a few simple things-
Hydrate like crazy, and don't sock the food to them when you first get them. Let them settle in for a few days and then try a couple small prey items. Ramp it up slowly, they've been under stress and neglected for a while so feeding them heavily when you get them may sound like good sense but it's actually counter productive.
Quarantine in a simple enclosure and clean it religiously. Use paper towel, or no substrate at all so you can spot clean and manually break up parasite life cycles/reduce their numbers.
Leave them alone. Do the above, and nothing else. Let them settle in, get them hydrated, eating, and not under heavy parasite load and bulk of your acclimation is done.
