To offset the buyers or sellers that are unresponsive or miss appointments perhaps OfferUp could provide an escrow service where you could voluntarily bank a deposit to further reinforce a person's trust level on their profile. Say either a buyer/seller would have the option to filter users' on whether they have funds that are banked. If the user fails to follow through after 3 strikes(? community reported) the funds would be returned, they would be removed from the program and placed on probation for a period of time. I understand it's sensitive dealing with people's money, so that is why in case of a user not meeting expectations, only the offending user would collect their own funds. The additional countermeasures would penalize them. Just a thought to add a level of accountability in an anonymous environment.