Willo, you fail to mention wether it was cash or paypal?
Reason being is if he payed via paypal anything under £500 can be taken back for upto 3 months iirc.
If he paid by cash you are ok, just sell the item on.
Just be aware that he may crawl his deposit back via paypal at antime which could leave you short.
Although I can't see how it would work, this has the feeling of a scam: why would someone just give away £150? I wouldn't sell it until you have confirmation in writing, or at least make sure you can return the £150 if asked.
Chris, we have people leave deposits of £300 on vans then not come back or call saying they have found another elsewhere and to keep the deposit.
Sometimes its worth losing a few quid to gain a better item.
I Don't think there is any scam involved here.
Besides, thats the whole point of a deposit, so you know the buyer will not mess you around, they do mess you around and they lose their deposit, simples.