Also, think outside of the internet. If you really want to sell beats, meet face to face with artists. People like to buy in person over online.
Go to places where artists are: Open mic sessions at bars/clubs, hip hop shows, DJ at parties, ask to leave your mix tapes at the barber shop.
Always have your music on you. Play your stuff for people who will want to buy beats off you. Give them your contact information along with your phone and website where they can hear more stuff. And more importantly, tell them your working on new stuff and get their contact info.
Stay in touch with your contacts!