I drafted an email with the stuff I was willing to sell, then copy/pasted it into emails to all the above. Got some very different prices! In the end I went with WEX as I was PXing for new gear through them rather than cash. If you're intending to buy new stuff you need to check the prices they're selling at. For example WEX had an X-T2 with Grip for half price and a £££ trade in bonus which made what I was buying much cheaper than (for example) Ffordes. The valuation from Ffordes was better than WEX, but I'd have had to shell out more for the gear I was after.
In terms of "honesty" - WEX were pretty good (they valued one lens better than I did) but importantly, they kept in touch and the whole transfer of credit/new purchase was very smooth. It's not the cheapest option (Grey imports & selling on TP, Gumtree or eBay) but it's hassle free, safe, covered with guarantees and it just works.