I believe its my professional responsibility to advise someone of additional work that's needed. I can advise them of the severity of the work needed and the estimate then leave it up to them. If I don't then they'll probably bitch to the next guy about how they "Just had their car in for an oil change last month and why didn't they notice the front brakes were bad"... Lost customer.
Whats wrong with up selling when the work is definitely needed. Of course the customer should be on their toes because a lot of shops make their money on the up sell. They're giving the $24.95 oil change special or coupon away just to get a good look at your car and to take a crack at you. It takes all kinds.