Sorry about all the no-shows. I feel your pain. What I've started doing if I have to go out of my way to meet someone is exchange phone numbers with them. I know OfferUp frowns on this but since there's no way to rate a no-show I've resorted to this out of frustration. And you know what? People who are serious about meeting have no problem giving out their phone number. As a result, no-shows are way down for me. In fact, I've never had anyone stand me up who has given me their phone number.
OfferUp discourages giving out personal info like phone numbers out of privacy concerns but, truth be told, you can get a lot more info from someone's car license plate number than you can their phone number. And we all see each other's licence plate numbers when we meet.