Endusers are going to pay the highest price. Study sales on NameBio, and take note to the sales platform reported. There's your big players like Sedo, Flippa, GoDaddy, NameJet, and an active reseller market on NamePros. Most of us expect reseller prices though, so you're best bet is to focus on endusers if you want quality sales over quantity sales. Be aware of domains regged with similar keywords, and the domains ranking high in google for your keywords.
To the point JB Lions is trying to make, you don't go into a financial forum, say you're a stock broker, and ask what exchanges are out there to trade on. I am going to give you the benefit of the doubt here, and assumed you meant domain investor otherwise known as a Domainer.