Perhaps you should move on to some other app. The app has over 40 million users, so even IF 1% of users (40,000 people) screw up the shipping process, OfferUp would not be able to provide the "hand holding" support that is required to remedy the problem(s). The company has less than 300 employees and wonder how many of them are a part of shipping support? Probably less than 70 CSR's.
The shipping process does need a overhaul, since there are more than a few loopholes that scammers can easily manipulate by creating multiple accounts. This is why so many people have complained about the "pending review" process/wait, since OfferUp is attempting the check the legitimacy of these transactions via shipping.