I guess the main question is why he is selling, as long as he is not getting out of the hobby due to the tank not doing good. You just want to make sure he is not having algae or pests problems, as you don't want to add that to your tank.
corals can be dipped to remove pests, but bad rock must be killed off by drying it out and/or cooking it, before introducing it into your tank. Hopefully those are not the reasons for that sale, but is must know information.