Bank transactions over 10K get reported. If I roll into my local Chevy dealer and buy a $75,000 truck for cash, does that get reported?
Yes, absolutely. The same law that provides for banks reporting deposits and withdrawals over $10K also puts similar requirements on retail establishments that accept payments that large.
The same thing happens with houses. Someone buys an absolute dumpster fire in cash. Then they pay contractors to fix it up nice, beautiful appliances, tiling etc. The house gets sold and the money ends up all in the white.
I used to work at a restaurant that regularly deposited more than $10,000 cash per day. We never filed any IRS reports for that, maybe the bank did.
I bought a car a few years ago half cash, half financing. The dealer sent me a letter stating that they notified the IRS under their obligation to report cash transactions over $10K.