Try to put yourself in others ' shoes, how you feel if are the camera shop owner?
When the customer don't know anything about the lens, ask you can try 5-6 lens w/o any intention to buy..
Generally, you will be in for a bad experience if you try 6 -7 lenses at any of the shops without the intention to buy. Black face treatment is a commonality. Worse still, you may be cursed if you do this at the wrong store. What do you intend to shoot in the shop to try out the lenses? Ask the shopkeeper to run and see whether your lens can focus fast enough to capture the action or zoom in to capture the action at the opposite ba kwa store, etc. Doesn't make sense to me. Rent the lenses, go out and have a good shooting trip before deciding whether they suit your shooting style.