I gotta say he'd have to be mentally retarded to give you his ID if he really was trying to do a dodgy, depending on the postage type it may require to be signed for in person as opposed to anyone at the address and the fact that he is still making contact surely has to be a postive? I wouldnt say just because he is using multiple bank accounts it a massive concern either.
All I can say is make sure you keep on top of this, you've probably done yourself a huge favor keeping all the relevant information and correspondence as you have, hopefully it'll get resolved for you without it going too far with police \ courts etc.
Despite the fact that he's been particularly slow and poor with communication as many, including myself, have said, it does seem odd that he'd go rogue since he did have reasonably good feedback profile of nearly 50 deals, a large proportion of which he's been the seller.