Does this mean "never trust your own devices" or "never trust uncle Lee's devices"? I think it can be interpreted both ways but I don't know which way to go.

I interpreted it as "Never trust uncle Lee's devices". I know this is a late reply, but hope it helps nonetheless!

Well I interpreted it as "Never put blind trust in technology - it may (and will) fail!"

Yes, it works for both! It really depends on what you want to emphasize: the moral of the story or how fed up Ines is with her uncle's shenanigans.