Arbitraging fraud has always been PayPal's game. For the mass market of small-scale sellers there's a threshold, whre the cost of onboarding, verifying, underwriting and eating fraud exposure is greater than the revenues you could ever expect to make from them at their low volume. So these segments went un-served, same with many other segments of transactions or transactors. PayPal's model has always been to accept a…
Ebay and Paypal are full of scam. Simply it is thei best interest to keep this up because it generates revenue for them.
The optimal amount of fraud is neither zero nor "let it all through." Their "best interest" is a balance between allowing legit transactions to get through and blocking enough fraudulent ones that fraud doesn't become too common.