Paying with Paypal. If anything is wrong with the unit and the seller makes any problems, enjoy Paypal's buyer's protection. Worked very well for me once when I was ripped buying a guitar.
Unless they've changed the program since I got ripped off three years ago, Paypal's Buyer protection only covers the first $250. I paid $850 for a laptop on ebay, a laptop which not only didn't exist, but which the guy had sold to twelve different people.
After lots of aggravation, I got back $250.
Whilst the prices on ebay seem attractive from the states what they fail to tell you is that you have to pay VAT and Import tax to get the item into the UK. If you go on to the VAT and import duty calculator what you will actually pay for a secondhand/new unit is the same as what you will pay on a new unit from g66, if you buy from g66 you get all the support and fantastic customer service.
FWIW I was in the same boat as the OP a month or so ago and was trying to get an axe fx2 on the cheap from ebay/gumtree, my advice buy from g66 for complete peace of mind.
I have just "hit the button" and ordered a new one from G66. For piece of mind I have been swayed away from an ebay purchase.