My personal experiences buy from Audiogon are:
I preferred to buy local if possible, so you can audition the product and save on shipping.
If local pick up is not possible, pay by Paypal with funds drawn from Credit Card so you can dispute the transaction with your CC company with 30 days if anything does go wrong.
Get the person phone number so you can contact he or she to get a feel of the person you're dealing with. (This is very simple but often overlooked)

Good luck!