Well, I am an actual employee at OfferUp, @esc2010! Have been for almost 3 years now. I am passionate about our app and this community. It honestly pains me to not have a solution for you guys. I know that there have been several one-off issues related to matching names and bank accounts, or stories of users not using our pre-paid shipping labels which would absolutely slow down the payout process. Many times, there is a completely valid explanation for why the payout is taking longer, but unfortunately, I don't have the tools or ability to confirm this each time.
Ok, so - I have seen sellers close their account after accepting an offer. Buyers will ABSOLUTELY get their money back in this case and the seller account would be permanently removed.
A buyer is only able to cancel an offer before the seller accepts it.
When it comes to users attempting to defraud our shipping feature, we're incredibly strict and won't hesitate to remove accounts that attempt to do so. Users that regularly cancel shipping transactions will also have their shipping abilities revoked.