I recently sold my 70-300 L lens. I prepared everything ready for Ebay and then, at the last minute (and partly through Ian W’s experience) I gave Wex a try.
You just fill in the form on their website. I had a look at sold items on EBay and the Wex offer stood up well, especially when you consider the charges eBay make and the fact that the postage is paid by Wex when you deal with them.
So it is gone. Only drawback is that they give you a credit note (in effect), so you have to spend the money with them.