It's usually pretty tough to tell someone their bike isn't worth fixing. I've had customers literally dump hundreds of dollars into their Walmart Special mountain bike that have been sitting outside behind the shed for three years instead of wanting to buy a new bike. I also had a guy come in to the old shop where I worked with an old Schwinn Varsity that looked like it had been pulled from the bottom of the river and he only wanted new tires - "The cheapest ones you've got" - and I refused to touch it.

I'm usually just cut and dry with them, as I am in most situations. Not being a jerk about it, but being honest. If they don't want to hear it or try to skirt around it, they can exit the same way they came in.

It sucks to see someone riding a bike that isn't safe but if I try to help them and they choose to ignore it, it's really not my problem.