Disappearing emails from a used car dealer

For the first time ever I had my important emails about auto purchase disappear from my Gmail account. Only after a day or two of being there. Fortunately I printed the emails when I first got them.

What gives? Is the dealer trying to pull a fast one on me?

Since then I checked if it's possible to send disappearing emails in Gmail. To my surprise, it's possible with use of Confidential email option in Gmail. The disappearance can be set from 1 day to 5 years!

Have no idea why would the dealer do that. I made a deal and am about to fly to Tampa with a big fat check to pick up my car.