All I am saying is make an effort. If you believe and trust your realtor then ask how your realtor found the information out? Did your realtor call the agent? Did your realtor call the broker that the agent works under if that agent was not a broker?
Look, I have a client who has been heartbroken because he has been outbid on some offers. The latest was a foreclosure but the listing agent answered my inquiry as to who the selling agent was (buyers agent) and told me I could contact his broker to verify if I wanted to. That is the best I can do for my client and when the transaction closes I can verify the information.
There is not anything else that can be done.
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Look at your post and what you wrote. You made no mention that your realtor had told you this, nor have you made reference as to how your realtor found this out. The home was on the market 6 days before it went into withdrawn status. Did you make an offer on it? If you think there really is a problem then take action. I have another client who made a complaint to the BBB against a listing agent because that person thought the agent was not dealing fairly. This client also went to the Prudential office and confronted the broker about the situation.
The point is that of course they (the realtor in question) will most likely not tell the truth but you can take more action if you want to. I agree that we are helpless to that sort of crime. The fact of the matter is that yes this kind of crap goes on and the more people do to combat it, the better. It may seem like complaints to the DRE and BBB are useless but they do not go totally unnoticed.