What about buying a used or refurbished lens from B&H?
I am not sure if I have seen any Canon refurbished gear at B&H, not in the last few years for sure. If you want to buy Canon refurbished gear, then I would only recommend the Canon refurbished store. They will give you a one year warranty, not just a "guarantee" of some kind.
I think B&H has a fairly good and objective rating system for their used gear. I think much of it is a bit pricey, though. Many times they will offer used gear that is rated "good" that has an asking price that is more than what is being offered in the Canon Refurbished Store.
Check what the B&H guarantee and return policy might be for used gear. I've bought a used tripod head and a "hi-hat" tripod from B&H, and I think I had a 15 day return window, and a 30 day guarantee.
Good judgement needs to exercised when buying used gear. You must consider the source. You must consider the return policy, for which B&H has a good reputation. You must consider the cost/benefit of expensive gear without a warranty. You must consider can the used gear be repaired, if needed in the near future.
With used camera gear, there is always a risk of mold and mildew contamination. Canon's refurbished gear has that new gear smell to it, so I think the contamination risk is small to non-existent with Canon.
[EDIT]. If what you want is out of stock at the Canon Refurbished Store, be patient. Most of the items will be back in stock in a month, or two, or three. The "L" series lenses can sell out very quickly.