Dials - The thin line between cleaning and....

Hi,
another (rookie) question from me:
While looking for a new watch and finding interesting ones with dirty dials, I was wondering what would be accepted as a maintenance measure and where the - let’s say re-dialing starts when it comes to clean the dial?
For example can you just clean the dial somehow and have it still kept in the Original (collectors) condition)? Where does the re-dialing starts?

I have myself a couple of times carefully blown dust from the dial and removed small dirt spots with at damp cotton bud. Other than that cleaning the dial is pretty much impossible with good results in my experience.

I've never had the courage to attempt to clean a dial. A redial is generally done when the old dial is unreadable, or damaged to the point of no return. I once bought a vintage Breitling who's dial was completely unreadable. I sent it to International Dial and had it refinished.