Re:
Really sorry to hear about this. Rest assured that you won't have any bother with me and the Clockwork sale!
I think that you've been really unlucky on this one. I have to say that I've been scammed and otherwise ripped off and abused as a buyer and a seller on multiple occasions thanks to (routine) misuse of eBay and PayPal's buyer protection schemes, but when dealing on trust, on forums, and using PayPal gift payments, I've never had a single issue.
And at the end of the day, over the years I've quite probably paid more to eBay and PayPal in fees than the £800 you've lost. It's a gamble either way, but the house always wins...
Facebook obviously is a different thing altogether. I have to say I'm as surprised as you were at the angle the con artists have used to pull this, but in all honesty, the sum of money involved and the "it's for a mate" line would probably have rung alarms bells to me... that probably reflects badly on me - I think trust is better for your karma and overall outlook than paranoia.
And on that score, it seems to me that your karma is strong enough that you'll get it back one way or another. Don't lose heart.