I am currently looking to purchase the Canon 70-200mm f2.8 IS USM lens, and I found one on ebay for approximately $1,800. It is advertised as brand new, and has a US warranty. This would save me around $200, but I can't help but be suspicious. The seller has a 100% positive feedback rating, and not a single negative review. I asked how he is able to sell his lenses for so low, and he said that he is not an authorized Canon dealer and so he can decide his own prices. I asked the origin of his lens, and he claims it came from a retailer but he did not receive a sales receipt. Does this sound like a believable story, and would you recommend purchasing this particular lens? I would be suspect he is lying, but the reviews from other people are nothing but spectacular. Any advice is appreciated!