What is a house worth?
Just because a house is listed at a certain price doesn't mean it has to sell for that amount. Sometimes people list their homes too high, other times agents make the same mistake. With the right research, you can find out what any house is worth, which will save you money and even give you negotiating power.
Look at comparable listings. Find out what other houses in the area have sold for that are of similar size, age, and condition. If the neighbor across the street has a floor plan just like the one you are interested in and they sold their house for $100,000, the home around the block sold a couple months ago for $94,000, and the house next door recently went for $102,500, you can take an educated guess that the home you are interested in is valued in that general price range.
Condition of the home. The price of a home is highly dependant on how well it looks, what amenities it has, and what problems need to be fixed. For instance, there could be two tract home for sale with the same floor plan and one will sell for less simply because it could use a coat of paint. When you look at comparable sold properties, consider which homes are the most similar in appearance to the one you are interested in.
Research the market. You will have a better chance at submitting an offer below listing price in a buyer's market, which is when there are more homes for sale than people looking to make a purchase. On the other hand, in a seller's market, the cost of homes is rising, there are more buyers than available homes, and you may have to submit a higher offer to beat out other people who also like a particular home.
Consider your agent's opinion. Real estate agents are in the business of knowing what is happening in the market, how much homes are worth in the area they work, and can run comparable sold listings and even bring up current listings on the market that are similar to the home you are interested in. If you're looking to buy a property at a very low price, they might ask you to come up in the amount you offer. If the recent sales agree with them, it may benefit you to consider offering around the price they suggest, in accordance with the comparable listing results.