the white residue is from the dealer not properly masking the car before he polished it, Once that stuff hardens it becomes harder to remove (a steam cleaner is useful in those cases). Id remove the leftover with some alcohol, unless it was stuck in some crevices in which case id bust out the steamer. My cousin just bought a cpo and the dealer detailed it and there was polish stuck in all kinds of places.
The seats/steering being slippery is just the type of product they used. Something like 303 would give that same slippery, squeeky feel to it. It wears off. But if you want it gone now, you can buy an all purpose cleaner and wipe down the seats with it to get rid of the product, and then get something else to re-apply that wont leave that greasy slippery feel.