Could smart criminals just also run a Tor exit node, and just use it to blame anything that they get caught on?
A Tor exit node is just a tool used to obscure your location. Nothing more. So let's rephrase your question as such:
"Could smart criminals just tape over their house numbers, and just use it to blame anything that they get caught on?"
A Tor exit node is the last "hop" or "layer" before data exits the encrypted tor network.
So let's rephrase the parent's question as such:
"Could smart criminals just operate a package exporting company and just blame other people when they get caught for exporting contraband?"
The answer is yes.