Question about cleaning coins?

Boy you are going to get answers all over the place on this subject. PCGS and NGC will grade coins that have been professionally "dipped" with solutions like Jeweluster. I'm not sure about Verdi-Care or Nic-A-Date.
I think it is best that you do not attempt to clean your coins. The market has changed from the old thought that a bright shinny coin is better. We are now in a market where an original unmolested coin is more desirable and will command a higher price.

Thanks for the comment Indian. I'm not looking to make my coins "bright and shinny", I'm more talking about removing a spot on a coin, a piece of gunk or a thin layer of gunk from a coin without altering the way the rest of the coin looks and without ruining the value. I'm also not going to try on anything worth more then a few bucks.

I've had mixed results with Acetone. when you say clean spots make sure they aren't verdigris. Unfortunately, acetone doesn't do much for it.

Every problem is specific to the coin and must be treated individually. Don't take generic advice telling you to use this or that. Chances are they won't work or, worse yet, they ruin your coin(s).

Also, there's a BIG difference between conservation and cleaning.

Cleaning = Market unacceptable
Conservation = Market acceptable

Keep in mind, some coins are not worth the effort of conservation. If you're going to take on a project, make sure it's worth the effort in the end. If you have a coin you feel is worthy of the process, post a picture of it here so we can get an idea of the nature of the problem. We can give you some guidance once we know what we're dealing with.