I'm not sure, but I bet the term for it is "scam".

Maybe you could "deep clean" the crumbs out of a toaster with some sort of special suction tool, but the inside of a microwave oven has baked on splatters and I don't see how a suction device would remove this stuff. One way to clean out a microwave is to remove the turntable, turn it upside down, and put a damp sponge loaded with warm water & detergent on the worst of the caked on residue. Then walk away, and let it sit for 10 or 20 minutes. Eventually, the material you want to remove will soften, and it can be wiped away.

I wonder if it might have been some sort of professional steam cleaning service.

Something similar you can try as ericwi recommended is placing a bowl of water in microwave, microwave maybe a couple of minutes until water is steaming, then leave for approx. 10 min. Wipe clean.

I've cleaned my oven with the help of my vacuum (with attachments). I scraped the burned black stuff off the inside of my oven using a putty knife, then vacuum up the carbon-material that flaked off. Then follow with a good regular cleaning of the oven. I use Easy Off , the kind meant for cool oven cleaning. I think it comes in a blue spray can.