it depends really, i find if you sell a flashed one its best to throw in some games as the discs cost like a £1 each if they are decent but if you throw in say 10 games it increases the price by more than £10 as people place a higher value on them... but yeah i think if you have the controller, wires box n shit then say 10-15 games... maybe even let them pick some you could get £250 depending on its actual condition
just depends on the person looking at that time and what they think its worth i guess