I had to laugh when my friend told me she treats her car like her hair! In other words she changes out the shampoo every few washes, even though there is no logical reason for this to make a difference.
Your friend sounds a little quirky but it's a harmless hobby to have! If she rotates products then at least she's not losing out financially. Maybe she hasn't found a product she really likes yet.
Going to different gas stations each time is fine but I don't think it is advisable to use different brands of oil. But I think it's OK to use different products for car washing.
