There is no trouble to make it work with a CPU of some type, but "who pays for the service of finding out that the CPU is faulty?". The engineering time until you have *proven* (not just tried) that the CPU is at fault and the card is A-OK can easily be more expensive than the card itself.
So now we have a customer who purchased a card w/o CPU for maybe 400,- EUR. He also spent some amount for a CPU, puts both together and finds that it does not work.
The CPU came "from eBay", and the seller won't answer eMails. So the whole thing goes to me, and I'll do a 500,- EUR job proving that the CPU is at fault, and the card only suffered minor scratches, but works fine.
Customer refuses to pay, even threatens me with a lawyer, so I have to pay for all shipping. He then executes his right of revocation, leaving me with a scratched card, shipping cost and unpaid engineering work. If worse comes to worse, he even claims that my card has damaged his 200-EUR-CPU and makes me pay for that.
Not my kind of business.