Comment by jacquesm
You have a presumption of innocence up to a certain amount. After that there is a - minor - burden of proof. Not a single time that this happened to me did any of this appear to me to be unduly burdensome or invasive, and whoever did the investigation went out of their way to state that they did these checks as a formality, not because I was suspected to be in any way out of line. I don't recall it ever taking more than a few minutes (if that) either.
If I showed up with 50K in cash at the tellers window or a local notary to pay in part for a house tomorrow morning though I would expect the conversation would be an entirely different one.
50K cash is under the real value of the $10k CTR cutoff when congress passed the bank secrecy act (around 85k in current USD), so you can see how this slippery slope of the erosion of the 'up to a certain amount' has only gotten worse.