New or used?
It really depends on how much you trust the seller and their description. I brought mine second hand. The seller advised he had had the IS replaced under warrenty within 1 year of its purchase. I can't remember how old it is but it works just fine and as it should. I also brought my 300mm L IS f/4 second hand and that's ancient but it works just fine. If you can't view the lens ask lots of questions around dust, scratches, fungus, how used i.e. surfing photography query sand and salt water. Check how other people have found the seller.