I've bought a coupla cars via the internet (one from eBay), all sight unseen. Couldn't be happier.

I spent a lot of time talking to the owners over the phone, composing emails, looking at exhaustive amounts of photos and getting some sort of guarantee that if I didn't like the car, I could: A) Get my airfair refunded, B) Get my deposit back C) Walk away altogether. It really depended on the situation, but in all cases I had at least one of those as insurance.