I've read that whole thread about the Gluhcheff's, and what a mess it's been.
If you really want to be safe, deal with the parents directly for the final part of the deal.
That way you can explain to them what is involved in the transaction, both monetarily and in the animal(s) specifically.
As someone who forged about 150 notes in junior and senior high, I can say that just getting a letter or fax won't absolve you of any responsibility. Any kid could fake one.
And a kid can also use their knowledge to misrepresent what the animal is when asking their parents if they can have them. "Mom, I want a reticulated python from this site, you can look them up under Python Regius < wink wink >. They only get to be 4 feet long! < snicker >".
Not like that will happen with Geckos, but it's just something to think of with any transaction
PS. When I was 11, I almost DID buy a reticulated python. The seller heard me telling my dad I wanted a snake in the mall, and he offered to sell it to us for 300 dollars, saying it would only grow to 4 or 5 feet, tops. Good thing my dad didn't have the money and blew him off