Is it safe to buy an iphone 5 from ebay/amazon?

I want to buy an unlocked one thats about £120 cheaper than on apple.com, why so cheap? Is it safe? Will i still be able to buy ad-ons?

1.Yes
2.Free market economy
3.Yes

Hi

yes its fine, provding the seller hasn't blocked the phone via the network.

I bought a second hand one from CEX in manchester and it worked fine for many months until i broke the home button, as it was on warranty they fixed it in 5 days.