Over the past 4 years, I've seen this come up a couple times. The main reason OfferUp doesn't work with a VPN is that we do require location permissions. Since location data was necessary to show community members items in their area, there will be issues trying to use OfferUp through a VPN.
I would have noooo clue about that! haha - just a Community Manager here, no techy background
I will say now that there may be a case to look into this again now that we aren't hyper local focused.
Couldn't you use GPS location instead of network location?
GPS for geo-location proximation will ONLY work with people on mobile devices WITH data service, but not for every user, as many people use the desktop mode in static environments or "free" wifi (ie...Starbucks, public library,etc) with other handheld devices.
Cloudfare only filters commercially available VPN IP addresses. I use my "diy" VPN and run all my traffic through it without any access issues. For less than $100, anyone can build their own VPN, as there is a plethora amount of tutorials online.