[mothered]

You should tell them that the CPU doesn't work, you have tried that on another Mobo and it doesn't work.

I mean wouldn't that make them check the CPU and find out that it's an Intel Core i7 2700k

If you say It's "the wrong Item", most likely they'll check It In preparation to put It on their warehouse deals. That Is, they must know the Item they're selling.

It's best to opt for "It doesn't work". The majority of times, they don't check and class It as a write-off.