Is it really worth the hassle of trying to get a refund over some fog lights? Will the foglights make or break the deal on the car or make the car THAT much better?
If anything I would just argue for a discount on an accessory.
My car had the M Performance Grill on it when I bought it, but it was not on the window sticker. The dealer realized their mistake and just ate the loss of 300$..
I would't say a simple typo constitutes a refund, especially on fog lights. Just tell them you want 250$ off the cost of the power pack
On my e90, the dealer did an oil change and reused the old crush ring, so my car leaked oil all the way home and I ended up having to add 2 quarts to it. I was pissed, the dealer almost destroyed my engine. They fixed it, and I told them I wanted a deal on a perf. exhaust and they offered me 20% off (about 250$). I say go this route.
Maybe if they had told you it was 340 HP and it ended up being 300 HP or something epic THEN I would ask for a refund.
It is well known in the USA M Sports do not come with fogs, there have been numerous threads on it.