Unless the house is work no more than 20k, you can't buy a house for cash without explaining where the cash came from, ie electronic trail.
Idiots at work though we'd win the lotto when we bought a brand new car worth over 50k. Yes, one person asked outright how much is the lease per month and when my husband told him we'd boguht it for cash he said you won the lotto.
We sold a car a few years ago and the bloke insisted paying us cash. We were dubious and thought even used notes notes to make them looked used could be fakes so we went to the bank together to deposit. The next day we got a call from the bank as we'd been with them for a few years asked us about the cash we told them we sold our car, they asked no further questions.
I recall mum and dad being paid in cash at work years ago as it was the orm and dad always had to have about 2k waiting arounf the house and when he went to see family more than a 100 miles he's take at least 1k with him in case the car broke down as my dad did not trust credit or bank cards.
If the person is splashing as put here, trust me it's only a matter of weeks before he is taken in as the police will get reports, they will do some background checks and any lotto or any other wink or money paid into his/their bank accounts will have a trail so they police will then decide if the money is legit or not.
You must trust me as if it's drugs money, soon everything will go quicker than it came.