One of the resources that all property investors should make use of is their local and the national Multi Listing Service, MLS System.
The Realtors in your area and nationally depend on the MLS system to inform other Realtors about properties that are available by registered Realtors.
This does not mean that every property in a given location will be listed on the MLS system it just means that Realtors have come together to pool their power over the buying and selling of properties.
It is also important to understand whether you are a buyer or a seller of which you are both these types as an Investor that the properties in the MLS system will require the use of a Realtor to make the purchase. This means that a buyer and seller fee of 3% on each side of the sale will be charged against you the investor. Since you will have 2 rounds of buying and selling, first at your initial purchase and second at the time of resale it is important to know that up to 12% may be eaten by Realtors. Often one side or the other will split the fee but there are times where as an investor you may open yourself to the full 12% which often can mean profit or loss in your flip.
But if you can find a property that is overwhelmingly a great bargain you may be able to still make a profit.
National MLS systems such as www.realtor.com are also a great way to get market information.
You can see what comparable homes or (Comps) are being listed for and since you are someone that plans your investments you will want to study the locations that you work in and see when houses are re-listed because they did not sell during the first 6 month contract or when they are listed with other Realtors or when they sit on the market long enough to require price reductions by the seller.
Most often then not a home that is listed for full market value by a Realtor is not a great investment for a house flipper because you need to buy property well below market value to make your profit.
So, Contact your local Realtors and find out what MLS system they use and then use the system to your advantage.