Tips on detecting coin cleaning

I've just begun my coin collecting journey, in which I am very weary and paranoid about getting a cleaned or otherwise "non-true" coin. As of now I have purchased two mercury dimes, in which I am fairly confident one hasn't been cleaned (link). I know that buying coins off of E-Bay and other online sites isn't optimal, due to pictures not being nearly enough most times to tell, but as of now that is the only way I can purchase coins efficiently. That being said, I have recently purchased a 1942 mercury in what is to be said fairly nice condition. I was wondering if anyone could tell me if this coin has been cleaned or if the marks are just from everyday abrasions. Thanks much :)