Buying used has the potential for getting a real bargain, but has increased risks. You can reduce those risks - if you are knowledgeable, careful to check the bike out, but you'll never entirely remove them. I have a 2010 spesh allez elite. It was £799 new, £699 end-of-season sales and I got it on
ebay for £543. The seller claimed it had never been used, and I tend to believe him - the plastic wrapping hadn't even been taken off the bar tape. So I saved £150 and really like the bike, and it has worked for me. Yet it's beginning to show signs of wear and tear. There are stories about very good service from specialized where frames fail. That isn't open to me - as a second-hand owner. Used value is probably about £350 so a £200 drop for me in 16 months, but about £350 or 50% for the new owner.