The delay in delivery is unacceptable in itself, particularly considering he gave a date of 90 days. Just to give Mark the benefit of the doubt, I have heard "horror stories" about the delay in obtaining CITES papers. In one instance an individual had to wait 6 months to receive his. Knowing this one shouldn't state to the buyer that they can be obtained in 90 days just to secure a deposit. Furthermore,
"IF" there was going to be an initially unforeseeable delay he should have immediately notified the OP of such. By not doing so without the conformity of the OP, he is at fault for not delivering what he owes in a timely manner. Anyone can have problems of their own, but when they have time to post other ads they should also inform their customers of the situation. It is lack of communication that breaks trust and not delayed delivery. Let's hope that at least he gets back in touch with you to explain what's happening.
I would give him one last chance by notifying him by phone or e-mail of what you are going to do if you don't hear from him. I know, I know, you have given him plenty but one more won't hurt; hopefully all you want is to have this resolved before attempting extreme measures.
Tell him you are giving him "X" number of days to reply to you and if he doesn't, then you will file a complaint with the Internet Crime Complaint Center @
http://www.ic3.gov The best way to get his attention would probably be to reply to one of his ads in kingsnake.com. One other thing you may want to consider before sending the formal complaint is send copies of your e-mail notification to kingsnake.com report abuse link:
http://market.kingsnake.com/abuse.php?cat=32&de=
If according to them your complaint is valid there's no doubt they will look into it and maybe even freeze his account with them. He has refused to contact you so regrettably he leaves you with no choice but to do this.
Regards and best of lucks.