If he's not going to tell us what he used he shouldn't have posted in the first place. I think he's trolling us.
A local dealer told you that cleaning a coin with baking soda didn't harm it? You may not be trolling us, but he was trolling you.
baking soda ? really. scratch city. that's a dealer I would have nothing to do with. geez. really ? OMG. do NOT use baking soda!!!