Doing it for his current employer would likely open him up to liability regarding embezzlement.

But it’s not a bad idea, the margins for PC building is really low for the general public though.

I don't see how a non-profit where the cost of the machine is the cost of the parts only could even realistically be embezzlement.

That is a very common way embezzle money. Well not the PC business, generally you pick something that looks higher margin and/or harder to get into, but really anything will work so long as it looks like a legitimate business that does something real. The scam is easy: buy something cheap, and charge a lot of $$$ for labor or support costs. It is very easy to hide overhead that can be go back to you.

You also typically are not directly involved in the business - that is both too much work and too obvious: instead you get your brother-in-law/uncle/cousin/... to start the business so it looks independent. Then the relative does expensive family vacations, football games and other such things that you happen to be invited on along with all your friends in common. (that is you need to make it look like money is never given to you, but because it is paid for you save a lot of money).

The other common thing to do is a charity. If a politician's family is in any way involved with a charity you should assume it is a scam - the charity might otherwise do good work but the family member is there as a way to hide bribes. (again, the money never reaches the politician, but it reaches family members who the politician wants to do well). This of course makes life hard for honest family members of politicians - everything they do looks like the politician (not them!) asking for a bribe.

It's not that it would be embezzlement, it's that it pattern matches to embezzlement. People with purchasing authority generally can't choose vendors they are involved with because that's such a popular way to steal money.