I have bought and sold on both sites and I have found both sites to work well. When I am looking at high end stereo equipment then Audiogon gets my interst. I look at the feedback on Ebay to see what the character of the seller may be like. This sometimes can put up the red flag. A scratch on a component can be tolerable if the purchased price is a great deal even if the buyer was not aware of the issue.
Kevyo
Kevyo