You need to hire a commercial Realtor that specializes in apartments. Commercial real estate is a highly fractured market and there is rarely a centralized MLS system available with all listings like there is in residential sales.
Look at some of the larger brokerages such as KW Commercial, CBRE, Trammel Crow, and Marcus and Millichap.... more
My experience has been that fixing up a house over selling as is will generally be more profitable for the seller.
Keep in mind, however, that it also depends on what it is you fix or update. Some fixes will garnish more return for your dollar. Generally, remodeling an outdated kitchen is number one on the list. Putting in a pool if one wasn't already there would be last.