Your real estate agent should be able to find comps and help you figure out fair value for the property. From there you can evaluate a price you are willing to pay. Your agent may want to ask them why it is advertised for less elsewhere. Did you see the mls? Make sure your agent is giving you the right info or find another. The bank may have been evicting tenants, doing repairs, or just slow to get it to market, so that part should not be a concern. 90 days listed though is a long time for bank properties implying the price is high.