I've just sold a number of items from my Canon setup in three tranches, and got quotes from
MPB and WEX. WEX were consistently higher than
MPB on every item. Not by a huge amount, 5-10% approx. I felt the prices from both were fair - they have to check items, advertise, resell and presumably pay or charge VAT as well. The WEX values being higher, compensates for them being PEX credit (well, it did for me). I've picked and chose what I buy from WEX using the credit, as they aren't always the cheapest out there, but for some items, they are competitive. For every item I sent back to WEX, I got the value quoted. I was accurate with my descriptions I thought. The ones I had concerns about were the "Like New" items. It's very hard for something to be 2 or 3 years old and be "Like New", even if it is "minty". I do keep every twist tie, every bit of cellophane in my packaging though from when stuff was new, so it's as new as it can be. I noticed my EOS-M had slight marks on the sides from the funky clip on camera straps, but hadn't noticed that until I was packing it up to send. I described it Like New, so was expecting an issue, but none at all. There was only one item that was problematic, and that was a 24-70L which I'd described as "Shows signs of use" - it was 13 years old and my most used lens, but was still in good nick, albeit the hood looked like it had done a few rounds in the ring. Anyway, the issue was that they'd quoted me for a higher condition category by (their) mistake. Fair play to them, they honoured the higher price they quoted me. All in all, I was very pleased with their service, and I think if I'd wanted a cash sale, MPBs would have been fair too.
The huge advantage is that both were quoting prices higher than people on here normally wish to pay. So it's well worth getting a quote as a collar below which you won't sell on here and it protects used values a bit. There is a lot of someone sold a lens for XYZ on here, therefore I'll only offer XYZ- £50. Can't blame anyone for trying, but at least you have a fairer sales option in place as insurance and evidence of true market value.