I would say tread carefully.
Even if the estate agent had nothing to do with this potential buyer (who could be a time waster - how are you going to check him or her out?) you might still have to pay the agent a fee. Check your agreement.
It could be that this guy is an opportunist who discovered there were no offers on your house and decided to make a play. Nothing wrong with that, but my own instinct (especially if you are locked into a contract with the agent) would be to tell him to make his offer through your agent - assuming you are happy that you have a good agent. Then let your agent do the work. A good experienced agent (if that's what you have) will sniff him out and soon discover if he's a genuine buyer.
Then again, if you are not locked into paying a commission to the agent, and you're satisfied he's genuine buyer, and you are happy with the price, why not go ahead?