And that would violate both BMWs Trademark and Patent, which at least in Switzerland could mean having to pay BMW damages and get fined for importing counterfeit goods.

good thing that it would be a chinese copy, and thus, not subject to switzerland law. So i wonder if chinese law recognize this patent/trademark for a screw?

IANAL, but as fas as I know when you're importing it from China, you are subject to local laws (and may pay the fine for importing a ccopy of a trademarked product).

Their point is that there's a possibility that Swiss customs fines them and confiscates the "counterfeit."

Maybe, the problem is that customs are not opening every package and as long as manufacturer won't name the copy as "screwdriver for patented BMW screw" but something more like screwdriver SN-2249 then how customs would know what that screwdriver is for?

What's the reality of that happening though? I feel like they have bigger fish to fry than going after people for buying one screwdriver bit.

Anyone with a mill could fabricate something to fit that in a short space of time.