i think he's just got carried away with pound notes flashing in his eyeballs... he obviously had a lot of calls when it was on for 350, then doubled the price and had no offers, now he's settled on half way... hmmm....
i did call him when it was re-listed, and he seemed fine to talk to, but then i changed my mind about going to see it. i don't think its a scam, but the guy is obviously not the most reliable (trustworthy?) person. the item itself seems to be for real. caution advised!
gumtree is full of this nonsense.