Is it illegal to clean money?

Answer 1

As a general rule, no.

If you just want to clean the money up from spilled food, drink or other foreign substances, clean all you like.

If you propose to clean coins to make them more valuable to potential purchasers, you are more likely to damage the finish and reduce or remove any collector value they may have.

Cleaning or washing banknotes to make them more appealing to a potential purchaser might be considered to be fraud. If the potential purchaser realises that the note has been washed, he will probably not buy it.