Anyone come across something like this:
I did an inspection yesterday and went to test the microwave oven. When I opened the door, the microwave turned on and the turntable started rotating. Closed the door and it turned off.
Nope, Weird to say the least.
Yes, it’s broken…
Is that it? 
Is that all you have to say David? LOL!
I would say it’s broken 
First time I have seen that
No Roy, that’s not all I have to say about that, but that’s all I’m going to say about that… Forrest Gump is my mentor!
Yes, I used to service and repair commercial kitchen appliances but…
Monitor!
WHO is to monitor: The potential purchaser
WHAT exactly is to be monitored: Their skin
WHEN (how often) is it to be monitored: After opening the microwave
HOW (process) is it to be monitored: Visually
WHAT is the person doing the monitoring looking for: Burning
WHAT do they do about it when it occurs? Call a physician, discontinue use of the microwave.
Yes. Note the problem and make a recommendation for replacement/repair as needed.
Simple.
Now, if your question is what is causing it, a simple google search may give you your answer:
“when i open the microwave door it starts”
;-)