Venmo also has buyer protection. You have to turn it on to get it, and the seller has to pay a fee, which they may ask you to cover. I understand that local bike shops will also agree to act as an escrow agent, although the one time I tried to do that they were scared of the Cruzbike, never having seen one before.
I personally wouldn't recommend buying anything from an unknown person without buyer protection. The first Cruzbike I was interested in buying, the seller wouldn't send it unless I mailed him a paper check, and then he would send the bike once the check cleared. I'm pretty sure the guy was legit (I looked him up) but even then it's a bad proposition. If he'd received the check, cashed it and then got hit by lightning before shipping the bike, I'd be out of luck. So I got my S40 from someone willing to use Venmo.
I really like that we have a community marketplace for Cruzbike riders, but 'buyer beware' should always be the rule for anonymous transactions.