I too won't ride a tuk-tuk unless there is no other choice. There is, of course, the safety concern - even a minor fender-bender can easily eject you. Along with that, there is no set price and no meter on any tuk-tuks that I've ever seen, which opens the rip-off door wide open. I too have been on tuk-tuks on which the drivers, rather than just take me to my destination, try to get me to go on some sort of tour or try to get me to let them take me to some sort of venue that I have no desire to go to, but they get a commission when they bring in a customer. Also, I don't like the sloped roofs. I can't see anything other than out the sides - no front view at all except for the driver's head and about two meters of street in front of him.
In other words, for me, no thanks.