I was going to use the Costco program. The first dealer they attached me to was clueless and just kept throwing numbers around. I said that isn't how this pgm is supposed to work. There was not a Costco in the area, and maybe I was the first match they had. Enter replacement dealership. They knew exactly what the price would be, no hassles. But I did email a few other dealers and ask for their best price. Those were lower. So I did ultimately buy from the dealer Costco sent me to, but not at the Costco price. It was the end of a model year. At the beginning of a model year it might be the best deal going. At the closeout time, it was not.
If a buyer isn't going to negotiate and search for the best price, it would be a very easy and stress free way to purchase. You will get a good price. If a buyer is cut throat and as tenacious as a spider in getting the lowest price possible, then it isn't going to give you that.