I'm not sure free will is a total illusion but we definitely make decisions on cruise control all day long.
The gas station is actually evidence of this: literally the utility of the product does not change, but more revenue ...
I think maybe it's an offence to Engineers to posit that they are not 'in control'. It takes some right-brain thinking to get this it's all a little counterintuitive.
But it's definitely reality. For the quickest possible introduction to really odd marketing concepts that are true, I'd recommend the '22 Immutable Laws of Marketing'. For an Engineer, it's like getting hit in the head with a frisbee.
That is exactly why brands use bright colours. It appeals to the part of the brain that evolved to recognize ripe fruit, for example.
As uncomfortable as it is to admit that these things may influence our behaviour, it is the reality. No person is completely immune.
Free will is largely an illusion. We act on impulses, then the conscious mind comes up with a plausible explanation for that action.