Criminals are perfectly willing to put time and effort to create fake accounts or just buy stolen accounts.
On eBay, yes, it was pretty easy to play the "Sell a bunch of stuff for 99 cents and then pull the big scam" game. But none of the widely-publicized cases where PayPal has basically attempted to wreck the lives of startup founders fall into that pattern. These people have all had independent web sites selling actual products, and/or a background in other ventures that could be checked if PayPal were to spend 5 minutes doing due diligence on them.
1) Run a legit business for a few months
2) Build up credit history with suppliers
3) After a while, buy a huge amount of stock on credit
4) Sell all of the stock for cash at massive discounts
5) Disappear with the cash, leaving a pile of unpaid debt in your wake
Someone looking to put one over on PayPal is not going to do all that crap. Sorry. I need to hear some actual examples if I'm going to change my mind.
Simple due diligence will either eliminate the genuine criminals, or it will not. If five minutes' worth of due diligence by humans fails, then so will any conceivable AI algorithm.