Take a look at the bid history, it suddenly jumps from circa £375 to £1120 - I suspect its someone looking to disrupt an auction.
The seller sets his stall out well and explains the pros and cons of unlocking. Where I think he's a little 'economical with the truth' is that he compares the cost of buying one from him with buying on in the UK on o2 and signing a contract.
Now, if you have no intention of being on an o2 contract, you can buy one next month for £269 and not activate it, then unlock it - hardly the same as the £900 he uses as a comparative figure.