Why would a real estate agent not want to do business with a second party investor?

I was told that if had a few preforclosure properties that i'am trying to sell,that a real estate agent would'nt want to try and bring people to my properties... On average there would be at least 20 to 30 thousand in equity on each property... I was told that the agent would get in my way or the other way around... I don't see how if there were contracts signed to prevent that from happening.
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Edmonton Real Estate|Real Estate in Edmonton