I'd get a couple more valuations done and see what the other agents say. If agent 1 has a developer in mind looking for houses to do up, and your mate is happy with the price he should take it. Nothing wrong with a chain free quick sale to a builder.
All agents will have builder/developers asking them for a heads-up on any potential projects - again nothing wrong with that, it's the agents job to link buyers with sellers and vice versa.