Most cash these days only takes a few hops, say you go ATM then send those bills out without spending locally and getting all new local bills, there's a high degree of co fidence that you mailed your cash since it all of a sudden ends up across the country.
Say you repeat this pattern and use the same seller often, then they have a decent idea that you're sending cash to buy something.
This is resolved by using cash more locally and sending bills you've recieved as change. This is why I like to spend $100s then buy XMR with my 50s and 20s.
