Ask for references from the hobbyist, then follow up and contact the provider they use as the reference. In addition to references, many providers use alternate methods to verify the hobbyist is legit ie confirming employment. You should also consider joining p411. The guys there are given ok's from providers they've seen and go through a rigorous screening process.
Here is a link that describes how you become a verified provider on ECCIE.
http://www.eccie.net/showthread.php?t=455407
Feel free to pm me with any questions.