I've had a couple of good deals. I go the 135mm f/2 from Canon's eBay Outlet shop, refurb for £680, instead of the usual £900, with a full Canon 12 month warranty. But a couple of years ago, I also paid £2800 for a mint 300 f/2.8, used twice, when it was selling new for around £3800. About 75% and 74% respectively.