Sorry for your bad experience, scammers are the worst. Don’t let it sour you on 2nd hand purchases in general or especially on the Merason which is a fantastic device. Sounds like you did all the usual things to be responsible so I wouldn’t feel too bad about it.
Paypal used to be horrible but now surprisingly good at protecting buyers. I would actually worry more as a seller nowadays. If I send a product, buyer says box arrived full of rocks with no product inside, I feel like Paypal is so focused on buyer protections that I might lose that dispute. I never worry as a buyer though.
EDIT of course make sure to always use regular paypal, not friends and family unless they actually are friends and/or family that you know personally.