That's because some folks think that logging out is turning it off. Or putting it on sleep mode (they press the power button a laptop, which has the "press power once" set to sleep or hibernate) and then logging back in = restarting.
When I worked a help desk I wouldn't ask the person to reboot. I'd walk them through it as if it was a troubleshooting step. If they balked, I'd blame it on process as necessary for me to generate a ticket to another team if necessary. Alternately, I'd remote in and just do it myself. It's not that they don't trust "you", it's that someone, somewhere, sometime, *didn't* reboot, said they did, and wasted 30 minutes of their time.