Quoted from YeOldPinPlayer:The same guarantee you had if the game never showed up.
Risk management is the key. If you're relying on the profits from flipping this game to pay your rent you'll take more precautions than if you would have used that cash to start your next bonfire.
Vid's guide has some good info. Escrow.com is one option. https://pinside.com/pinball/forum/topic/how-to-not-get-ripped-off-in-pinball-vids-guide
Recently used escrow.com for the first time. Not the cheapest option out there, but it was a pretty frictionless, fast, and secure transaction. I would definitely prefer to use them over a system like PayPal.