You don't need to convince me that OP messed up here. Obviously he should have imported the key, checked it worked, and then moved any coins to a new address under a key he controls. But he didn't do that, so he is left with the situation he is in.
Which is pretty much the same situation he would have been left with if he would have checked originally. A useless private key and paypal won't do anything to help and the seller, if we assume them to be a scammer, won't do anything either. I get how you are against using paypal to buy crypto but it's safer to do that than to buy crypto from a 3rd party USING paypal as the payment method, don't you think? Nowadays, i mean. OP didn't have that option back then.
where does it say they're going to "fine you thousands of dollars if you say things online that they don't like" ?
You can read the rest of the thread I linked for details. Anything that some unknown entity at PayPal deems as "
false, inaccurate or misleading" is classed as a restricted activity and can be fined. Pure censorship.
And you're wrong. I'm not going to go argue in that other thread but you're not understanding their terms and conditions. just because they classify something as a restricted activity doesn't mean a fine would apply to it. they can hold someone's funds for 180 days and then it requires legal processes to extend that longer. but there's no $2500 fine that they can just apply to anyone that engages in a restricted activity. so get your facts straight.

no one is going to get fined $2500 by paypal for saying things they don't like. it's not part of their terms and conditions. so if they did that then they would have no basis for it.