@JuliaO1If it was a cash transaction, I'm not sure how exactly OfferUp would get your money back.
It is on you to test every item before committing.
Test a washing machine you say?
Yes. While it may seem unortodox, it's best to test everything whenever possible.
If they don't let you, any decision you make thereafter is yours alone — you are not forced to buy items.
You can file a police report if you so choose.
If this potential scammer is meeting from home, it could help log his activity for police to look over and make an arrest in the future.
OfferUp is not responsible for the way people conduct business.
How did craiglist users deal with this type of situation if they had enough info on a person. Small claims court, most likely.
My advise is you should buy larger items (such as appliances) that require an investment at a retail store instead ¯\_(ツ)_/ ¯
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Just remember, the majority of users are honest people.
Learn from this experience and find ways to avoid it down the line.