work at a repair shop. random motherboard issues I'd probably put his CPU in another motherboard and or another CPU in his motherboard so I could get it diagnosed. I'd probably stop what im doing at that point and call him with repair options and prices. sometimes they don't answer and walk into to the store instead and say no i don't want it repaired but I want my computer now now now. if it's my day off someone else will have to put it back together. they might not know that I had another CPU in their case for diagnosing if it's the motherboard or cpu as it could be either.

this senerio isn't common probably had it happen to me once a year or so. the senerio is usually we gotta reassemble it and you can grab it in an hour or 2 or tomorrow when the repair person is in but sometimes people don't want to wait.

an i7-7700 instead of an i7-7700k isn't worth the hassle of this to make be make 25 to 50$ extra.

it's probably a misunderstanding or mistake and OP isn't even reaching out to them.