Used does not mean bad. The brand does have something to do with how long it will last though. A good MH
fixture is going to cost some bucks. Depending on what brand it is and whether or not it has actinics as well will also have an effect on price. Since this is a dual 150 I'm pretty sure they are double ended bulbs which means they have to be shielded so make sure they have the glass covers before you buy it. I would suggest replacing the bulbs regardless of what he tells you. New bulbs make a big difference as over time they will shift in spectrum which can lead to algae outbreaks.