Foul hands befoul all they touch. (Dictionary of English Proverbs/Thomas Preston)
There are other ways of saying this. Good cannot come from evil. The wrong thing for the right reason is still the wrong thing. Basically, don’t be tempted to accept something from someone you know has bad intentions most of the time. If someone has shown themselves over and over again to be up to no good, do not think that their dealings with you are the exception. If someone is dishonest, criminal, harmful, selfish, or any other form of bad character, stay away from their business. Just because you can “get a good deal” from a dishonest person does not mean you should take advantage of that deal. The end does not justify the means. Anyway, if you have to justify it, explain it, or hide it–don’t do it!