I have bought and sold $20k plus watches using wire transfers many times. As a seller, they are probably the safest form of payment you can receive after actual cash. Once the money lands in your account it is there to stay unless there is provable fraud like that the money was sent by someone who wasn't the account holder, but I've never heard of this happening. Banks take this stuff pretty seriously.

PayPal is a lot less safe for sellers, especially where credit cards are involved. I pretty much never accept it for large purchases unless the buyer is someone I know and trust 100% and they are willing to pay the fees.