This hasn't happened to me, but have come across a couple of items recently where they've been listed as BIN and a price of 99p. They were chilren's clothes in both cases, and I went ahead and bought them.
The first item was sent without question, but I bought the second item today and then got a message asking 'why have you sent money when the auction hasn't ended yet?' So clearly listed as BIN in error. Still waiting to hear back again, but have warned the seller she has another item on a BIN at 99p which hasn't sold yet.
As I've seen this happen a couple of times now, I was wondering if anyone else has had it happen to them when they're selling? Perhaps Buy It Now is being selected automatically when listing something without the seller knowing?