If the car is already properly waxed or sealed then avoid all wash n wax shampoo's and go for a pH neutral basic cleaning product, it'll not affect the wax that's already on the car and will instead concentrate on cleaning rather then trying to be a jack of all trades ;-) I keep this in stock for customers when I've done their car as it's just a good maintenance shampoo and cleans really well which is all you actually want from a shampoo http://www.valetpro.co.uk/prepare/concentrated-car-shampoo.html