Not really? As far as they know I could have spent that $8000 on a used car from another guy who then used that same money to buy a motorcycle. It's untracked for all the time it's not in the bank's hands.
It obviously could have gone through an intermediary, but it usually doesn't for honest transactions. If one of the two people is already a person of interest to law enforcement, a warrant can be called up to figure out exactly what happened. Added to other sources of information, like the new registry of the car or motorcycle, a pretty reliable history can be constructed.
Don't think in binary. Think in continuums of likelihood. Also, this isn't a new concept. It was covered by HBO's The Wire many years ago.
A motorcycle is a bad example, too, because there are licensing and registration requirements.