I read somewhere that ultimate business transaction is one where both parties feel like they've won. In this world of corporate takeovers, leveraged buyouts and forclosed properties, any deal where both parties can live with the outcome can be considered fair. Your friend could have offered $900 and been told $2000.
At any rate, it's pointless to feel guilty after the fact. The time to listen to your conscience is before you make a decision.
My $0.02
Rich