I have no idea who worked on his car before. There are companies in the US and Europe that have been disabling skreems for a while or whatever you want to call it. Most of the time nobody hooked up the correct wire back to their skreem. That may be the situation he is having.

Mercedes stopped supporting skreems for their own cars a few years ago. Anyone can clone key fobs or work with skreems. They sell the equipment and software online. I do not think any one you mentioned spent years trying to hack the system.