I don't think that will work. Flattening effects are achieved by intrducing flattening agents into the paint. I don't beleive I've ever seen a flattening effect adquately acheived by using sandpaper.
What he is doing is trying to hedge his bets. He is almost sure that you will not like the outcome of the "flattened" paint job. He'll try to simulate the look by leaving the surface a little rough (although I'm not sure how, I'm pretty sure what he's attempting won't work). You see, since he's sure you won't like it - all he has to do to fix it is buff it out more. This way he's got a backup plan that won't cost him anything if you don't like it. If he does it the way YOU want him to do, he has to resand and reshoot. Money and time out of his pocket - get the point?
The only way you are likely to get him to do it is to guarantee that you'll pay him if he shoots it like you tell him.
At this point, my personal opinion is to get another painter - one that deals with more custom jobs. Regardless of what you try to do with your current painter, I sincerely doubt that you'll like the outcome. If you pay up front, they'll likely not be as careful with your vehicle, because they already have your money - simple fact of human nature. If you just insist that he do it your way, he'll slow roll your job until you get frustrated and take it somewhere else. Remember, production shops don't make much money by having to do a car twice. They'd rather not do it at all, than to take that chance.
