Correction: Not all bank deposits over $10K...all bank deposits of CASH.
Possibly I am not grasping your point or Form 104? My understanding is that the seller ends up in receipt of the cash and may then deposit the cash to a bank account. That seller would then trigger Form 104 with his bank deposit and his name would end up on Form 104, not the buyer who used cash. If and when that person (the original buyer) sells the property, he can transact that with a bank account and avoid suspicion since no cash may be involved when he sells the property.