OK, so I'm a whinger and a pedant (great combination!!) But I've noticed that both "site unseen" and "sight unseen" are used to describe buying something (particularly property, obviously) without viewing it. My preference is "site unseen" - as in, "I haven't seen the site". But I can also understand "sight unseen", particularly for a non-property purchase, like a vehicle. As in, "I haven't had a sight of [thing]". So which is it?