If you're putting your house up for sale, you need to seed with a quick-cover type seed. maybe look at the kind that come with a mulch cover. Fertilize with a starter fertilizer and water! Hopefully it will establish itself quickly and your lawn will look better within a couple of weeks.
The heat of summer isn't the best time to get your lawn in shape.. grass is under stress because of the heat. good luck.
If it's not already started, you may as well not bother with it this time of year. It really only germinates well in the fall and spring. Even if you water it to death right now, it's not going to do that well.
You MAY get annual rye grass to germinate and that will get you through the first frost. But even that is hard to grow right now.