Many of my sellers or landlords ask me every year if they should winterseed (overseed) their grass or not. I always tell them that it is a good idea. In Arizona if you don't plant winter seed then the grass goes dormant and is brown and dry over the winter months. If a seller is trying to sell their house, it needs to be in its best condition and having brown, dull, dry grass does not show the house's best side.
October is the time to plant the winter seed so, if you haven't done it yet, get busy doing it. It doesn't take that long to plant the see for a typical Arizona lawn and in 2-3 weeks you will notice the difference and the buyer's will be happy you did in the months to come.