Hi welcome and let me see if I can answer this in strong enough terms.
Aaaarrrggggggggggghhhhhhhhhh Run do NOT walk away from that.
The customer is putting the onus on you if anything doesn't match up after machining. Let's say it is a $50,000 mold and the customer "thinks" it doesn't match the model, who is at fault.
You need to give this job to one of your competitors and let them get "rich" off it.
On tiny option that I would not tak,e but will suggest it, is if they gave you an .STL (or whatever) file that can convert directly to GCode to cut the mold (or whatever) then it may remove some risk. But, as I said, I would not do that.