Which is cheaper - new or 3-year old over 8 years?

I always question 1-3 year old MH's. Why were they traded or being sold. Always makes me wonder. I am sure there are more often than not good reasons but I get paranoid with used stuff. That's just me. BTW unless you buy a pretty high end unit, you aren't saving 100k by buying the same thing 3 years old.