well yea, the external parasites (i.e. mites) are easy to recognize and relatively easy to get rid of. the internal parasites (coccidians, worms, etc.) are the hard part. they're nearly impossible to detect with the naked eye. you'll have to check out the feces for that. as far as treating them, there are some remedies available, such as panacur or parazap, but from what i've heard from people around here is that you need precise measuring tools and whatnot. when i had a mite problem on my pietschmanni, i took it to the local exotics vet who gave it 3 shots of ivermectin at 2-week intervals. at the end test results came up negative. now im not sure what ivermectin is used for exactly, but i think it was for internal and external parasites. as far as what it treated internally, i dont know.
but as far as i know, one of the biggest hurdles after finding your gecko has parasites is finding a way to treat it. many areas dont have specialized exotic/reptile vets and they arent guaranteed to know what to do with your animals. my vet was pretty inexperienced with uroplatus specifically, but still knows what he's doing. i was a bit scared one of my spiny leaf tails would have dropped its tail when given the shot, but although she struggled a tiny bit when first handled, she took each shot very well. so if you or your vet thinks that he/she is the wrong person to treat your animal(s), see if they can refer you to someone better suited for the job. im pretty sure theres a webpage out there too with a listing of all the reptile-certified (or whatever) vets across the country. hopefully someone else can provide the link for that page.
hope you find good leaf tails and a good vet!