Buyer wants to pay me cash for part of the transaction

[Jack B.]

So an East Indian couple who are techies are interested in making an offer on my house but were curious to see if I would be willing to accept part of the payment in cash. For example: If the house is $1,000,000 they would offer me $800,000 as part of the official closing price and pay me 200K cash. 

From my perspective it seems fine as long as I get that 200K BEFORE the house closes escrow. Not like a day after....They said they'd be fine with that and we could get it drawn up on paper and notarized. 

From my perspective it benefits me just as much as it does them.

[Jerome K.]

Money laundering?  Tax evasion?  Seems sketch to me.