Suppose that products differ in their intrinsic quality, Q.  Q is
distributed uniformly between 0 and 1.  Sellers observe Q but buyers
only observe Q after they have purchased and used the product for some
time.  Sellers value products of quality Q at $150 + $200Q.  Buyers
will eventually value the product at $200 + $200Q.  What quality
products will be sold?

Ah homework.

I think you might have to make an assumption that buyers assume Q = .5
(since this is the average Q) before they purchase the item.  I'm not
certain that is the approach to take, but it makes sense to me.  I'm
sure you can do the math from there.