I just completed the process of selling my M1 iMac to SellYourMac. Don’t let the name fool you, they accept all Apple devices. This was the second item that I’ve sold to SYM and the experience was excellent both times.
What I like about SYM is that they communicate with you by email throughout the entire process. I got an email when my iMac was picked from UPS, when it was received at SYM warehouse, after it was inspected and condition confirmed, when the check was being processed, and when the check was mailed. I got the check about 3 days later, and it was for the exact amount of the quote.
Sure, I could have gotten more for my iMac on eBay or Craiglist, but I don’t like putting up with the fucking hassle. I did get a better price than Apple trade-in.