Yeah, it is all suspicion - Paypal (necessarily) keep details of their fraud detection algorithm very opaque.

And I too, have many happy clients who've never had Paypal issues, even ones doing some of the things I listed above.

_BUT_, if you think Paypal in general are _not_ a source of _major_ headaches for some people, "I suspect" (there's my phrase again) that you've not been here long. Paypal account freezing has a long history of being discussed here (and elsewhere). I've been through that particular drama myself, in fact I've got one client who it happens to annually when he starts accepting pre-orders in Sept for a book that gets printed every December...