That's true, but if you look up PayPal's acceptable use policy at https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&c... , you'll see that PayPal prohibits "payment processors to collect payments on behalf of merchants".

So, it's not just because they're worried about what you sell, you're not allowed to process payments on behalf of others at all ... which makes the whole Airbnb-PayPal thing that much more interesting.

By the way, here's a link to an article that does a good job of explaining why acting as an intermediary for other merchants is risky: http://www.braintreepaymentsolutions.com/blog/high-risk-mech...