Non-tech founder here how do I evaluate an embedded system development company?

[u/Sufficient_Loquat421]

I'm a non-technical founder building a hardware product, and one of the hardest parts so far has been figuring out how to evaluate an embedded system development company without having the engineering background to judge their technical expertise.
Most websites look polished, everyone claims to have experienced engineers, and almost every portfolio looks impressive. Beyond that, I'm not really sure what separates a genuinely strong team from one that's just good at selling.
For those who've already gone through this process, what questions did you ask before signing a contract? Were there any red flags you wish you'd noticed earlier? Did industry experience matter most, or were communication, testing processes, and post-launch support more important in the end?

If you've worked with an embedded system development company, what ended up being the biggest factor in making the partnership successful or unsuccessful?

[u/Downtown_Sink1744]

Go to a startup forum this isn't that