I have classifieds website. It costs just under $10 to place an ad for sale. Run until it sells. So i have people that pay but then after lets say a week or two they dispute it with paypal.
I think you need to change the Payment Processor as always I have seen that PayPal is getting hard for sellers like you. You can win disputes but this needs to have enough time and enough proofs.
You can't win... that's why paypal sucks. The only defense you can have is to offer a full refund so you can at least avoid the $35 fee that you'll have to pay for a chargeback. I suggest using clickbank as they offer refunds. You can't stop scams the least you can do is limit the expenses... Or possible use e-gold.com never used it myself but I hear good things and apparently they don't allow chargbacks.... so maybe look into that..
I know Some time if you open up a business Account with paypal It Protects You for Things Like this or things Very Similar To Stuff like this from occurring
The only way to protect yourself is to use payment proccessors that don't do reverse, chargeback. PP is not seller friendly.
I can say that the best way is to work with payment processors but you can always have paypal as an option - you can do fraud check yourself - its not hard and takes like 2 min per order. The thing is that there will always be fraudsters and you have to fight somehow. Having a charge back is a way to bad than being careful when accepting any payments. Good Luck!