Upload & Sell: On
A common scam is to buy something and then make a fraudulent claim it was never received and a chargeback. They will generally do it around the 1st of a month under the assumption that you have coverage for your mortgage but the check hasn't been processed yet. The typical warning sign is an insistence on shipping with USPS.
If you don't have sufficient balance in your bank account, then the chargeback will fail. I'd suggest having two completely separate bank accounts - one for paypal, then transfer funds out of the paypal-attached one to the other. Paypal can threaten this or that, but at that point you have a legal right to due process, can file suit, obtain an injunction, etc. Once they've taken your money in a chargeback the burden of proof is now on you to get it back.
Only ever ship with a service like Fedex that offers online signature verification. Paypal will try a chargeback and fail, investigate and discover you're in compliance with their rules, and bounce it back to the buyer's CCC, at which point the buyer will typically suddenly discover they actually did receive the item. That's been the time for me each time someone's tried the scam on me.
Shipping USPS is to ask getting ripped off. Never do it except for truly trivial stuff.