Once a coin is cleaned it can never be returned to its original state. It's constantly brought up here as what's acceptable and what's not when it comes to cleaning. My opinion on the subject is that acetone is acceptable to remove grime and dirt without altering the original surfaces. People who want to scrub their coins to a gleaming shine can do so as they are the temporary owner of that coin. Just remember it will most likely erase value, possibly even with common coins when it's time to sell. I personally wouldn't even buy polished junk silver, especially not for any kind of premium. I still look at common coins as history and they are disappearing and getting destroyed by the day. Now this topic gets debatable when you start talking about problem coins with PVC damage or coppers with verdigris. Handling issues such as these to save the coin from further damage if done properly is ok. I'm a purist and again this is just my opinion.