There's no problem with buying a used bike, particularly if you're buying a cruiser/tourer. Pretty easy to be able to tell if the bike has been taken care of or not.
I would, however, never buy a used sport bike. I've got eyes, I'm on the road all the time and I see the way people ride and abuse them. No thanks.
And I completely disagree with the notion that crashes are a "not if, when" scenario. I've been riding a long time and have never been down.
Ride with awareness, within your skill set, not like an asshat, expect the unexpected and you should be fine.
