Stefan,
I agree with some of the annoyances about OfferUp, but I have to say that it is clearly becoming the vehicle of choice for a lot of people in my area, at least those selling grills anyway. There are sometimes more unusual offerings on my local FB Marketplace, but trying to buy there is not as easy. Right now I plan to multiple list on CL, OfferUp, and LetGo. I don't have a FaceBook account and don't want one. So, for now, I plan to shop on FBM but not sell. CL is definitely fading but still a lot of grills listed.