I will put in my take. What type of sale? If it is a consignment gun sale I do not think there is any problem. If it is a PPT sale,there is no problem. If it is an off roster SSE sale,to my knowledge,there is not a problem,but DOJ has never came out and said SSE sales are legal or prohibited. The take I have on it is that it is legal. But that is not to say that the DOJ may change it's mind,or a new law may come out to change it.
I am not sure if a Dros sale of an exempt gun to a non-LEO will cause a delay in the transaction or not. I would think a incorrect sale would cause problems to the dealer from DOJ. DOJ also might to action to take the gun back from the customer.