One thing I would avoid is dealing with people who want to contact your via "in mail" on the site, then want to negotiate outside of the formal Audiogon "offer" method.
I had a guy who said he had all sorts of questions about the unit I was selling, asked for my phone number, called me, we settled on a price, then when he arrived at my home to pick up the unit, said he thought about it and decided to offer me $600 less. So I sent him packing.