If it's currently for sale, select your own Realtor; don't use the listing agent, the one representing the seller. Your Realtor then will help.
If it's not currently for sale, you'd probably be better off using a Realtor (though many investors buy properties without an agent). Even if a house isn't listed for sale, there's nothing wrong with making an offer.
There are plenty of threads here on Trulia about how to interview and select a Realtor.
Hope that helps.