I have an idea for an online marketplace in which third-party vendors would sell a certain high-value category of product. My concern is that the marketplace would be a target for fraudsters. A common form of marketplace abuse that I would anticipate, would be to "sell" something to customers, but to deliver nothing.
One way to mitigate fraud would be to collect certain identifying info from vendors, such as phone numbers or website urls. Even so, the profit margins for the category of items sold would be great enough, that it may be worth a fraudster's effort to get a temporary phone number or even a fake website, to create a semblance of legitimacy to scam customers. If banned from the marketplace, they may be able to repeat the scam by obtaining another phone number, email address, website, etc.
Another way to do it might be to put payments in escrow until goods are delivered. This sounds pretty good to me, but there don't seem to be many online payment solutions that support escrow, and of those that do, max escrow periods are short (I think it's something like two weeks for Braintree, for example).
I'd be interested to hear ideas on how to mitigate or thwart scams for an online marketplace that facilitates international transactions between clients and vendors.