Both Toyota and Mercedes sought Tesla's help with EVs for their California "compliance" vehicles: both the RAV4 EV and the Mercedes B-class EV had a Tesla frame, motors, batteries, and drive controller underneath. I don't know about the MB but the Toyota was rumored to cost roughly 2x the list price. In 2014, after Toyota made roughly 2000 of them (the minimum required by law) they stopped.

You can read about the common problems on the forums; lots of the same problems Teslas had in the time period (i.e. loss of all propulsion while driving, loud motor noises followed by eventual motor failure, etc) in addition to software problems bridging the two companies' systems.

All solvable but I'm sure Tesla prefers selling $100k cars better than selling $15k generic skateboards.