15% of what?!?Several say you should tip 15%. Not sure how that works!
How much faster could it really be though? It isn't like you are actually walking to get it.If you want your car to be parked close to the exit or whatever desirable spot so that they can get your car quickly when picking up, you tip upfront. If you don't care, just tip at pick-up.
It really depends on the place.How much faster could it really be though? It isn't like you are actually walking to get it.