Direct sale broker's commision

if it says it expires, it expired. they can't inforce anything 3 yrs later.

Is it possible that the agreement could expire and still have a valid clause that states that if the renter purchases the commission should be paid?

of course. what the fuck do you care, this is the seller's issue, not yours.

First, from what I can tell 3 yrs. later the 90 days is up obviously, so that's expired.
Second, the 6% would usually be paid by the owner, not renter.
I have put such into rental agreements and if there is a time-frame that trumps all.
Three years later I wouldn't worry about it if I were you.