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This is more about actually doing some background research before playing any game.
Everybody should research what the house edge is before playing any game. Anything above 5% is just a complete joke that should be avoided.
If you can't find out the information, ask customer support as they'll probably know.
Reading terms & conditions of websites, especially of those on which you're going to deposit amounts of money or to which you're about to send your personal documents, is a must.
But we all know it's way easier to check the little "I agree..." box and just blindly sign up.
Background research will not help with slots AFAIK. If a machine is rigged, nobody will tell you the truth. Otherwise, knowing you have a 80/20 chance in THEIR favor, way less people would play them.