I get what you mean. But what I was trying to say is that non-criminals would probably stay away from mixers because of the fear of being suspicious to the feds or whatever government entity. Anyway, maybe I'm just overly paranoid and overthinking stuff 
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.What are the chances that you will get the same dirty coins from the same guy multiple times that it could make the government actually think It's you? even If they do, they should be familiar on how mixers work and without proof, nothing much can be done.