swirl marks happen one because of improper washing techniques.
99.9% of the cars you see on the roads are washed by either
1. building watchman - one dirty rag cloth and a dirty bucket of water to wash a bunch of cars, you can imagine the damage it does to the paint
2. automatic car washes with those giant brushes that spin, same amount of damage as above
3. manual car washes, - a dirty rag cloth used to wash car, another dirty cloth used to dry car
to prevent them, wash your car at home using the 2 bucket method with the right equipment (all you need is $30-50) worth of stuff, like 2 buckets, grit guard, ,microfiber drying towel, and a very good quality wash mitt
see link below for how to wash a car correctly
http://www.detailedimage.com/Auto-Detai ... nd-Drying/if you already have swirl marks, you need to get the car detailed(wash, claybar, polish, wax) from a PROFESSIONAL, no cobone deals!! but find a shop that does excellent work