Whenever mine goes into VW for work I always, without fail, request them NOT to wash it. I've seen one of their technicians drop a sponge onto the floor which he then just picked up & put straight back on the bodywork, didn't even rinse it in the bucket (not that it makes a bit of difference!).
They do the rest to try & find some work to stitch you £70 an hour labour charge for, not out of the kindness of their hearts!!