I have not encountered any scams on offer up either but i know there out there. You have to use common sense. Check the seller or buyer out. How long have they been a member whats their rating and just always go with your gut feeling if it doesn't seem right don't do it
Always go with your guts feeling, stay clear of those sound too good to be true because scammers had practices thousand times over before they're perfect at scam people.
My best advise is for you to spend times gain knowledge how not to be victims of scammer. In this Community Forum there are many latest topics being dicuss about how scammer gain advantage of the buyer and seller alike.
Arm yourself with knowledgeable info so you're better off defending yourself if situation rise. There are scammer everywhere so be aware you'll be doing just fine. What are you using OfferUp app for buying or selling?