I very recently purchased a yellow tag Garmin MX 20 (Model # 430-0270-701) to pair with my Garmin 480. After much panel measuring, and trying to figure how to swap positions on my avionics stack without cutting into my custom carbon fiber panel, I reached the conclusion along with my avionics shop that it’s not going to work out. Why did I put the cart before the horse? The price was to good not to jump on it and work out the details later.

The pilot I bought this from said it was fully working condition, yellow tagged by the avionics shop, includes tray and connectors. He had no no issues with the unit, was fully functional upon removal. Screen in good condition. Firmware fully upgraded.
These are his pics. The unit is in excellent shape, no wear on the buttons and the screen is in very good condition.

Asking $650 for the unit, plus shipping.