^ I agree. I had something similar happen to me, but it was in the dog world (I also am highly involved with the world of canine competitions).

Anyways, this is how we would catch a "runner":
1. Call/text/email and leave a message with a warning of how you will contact the authorities, post his information online, and track him down via internet, phone or whatever.
2. Send a professional letter with warning
3. Call at different hours from different numbers
4. If you really want to catch them, then you could possibly hunt them down in person (I don't recommend this really, but I've done it before with success)

When this fails, go to authorities (the animal control is a good one, or other herp clubs/rescues/organizations near the trader's home), post in every forum about snakes warning about him, and possibly find someone who knows computers that can hack.

If the authorities don't want to help, then you can go on saying the animal's worth, how people who do illegal things with snakes can be related to worse criminal activities, they might release the snake causing problems with invasive species (if this is in the south), etc...

I hope this helps. Good luck finding your baby.