Gold plate Mint State coins, sell them for double and say on their ads "These are rarer than your average coins people!" In my opinion they diminished the value and defaced our nations currency. Wouldn't you agree?
They drive me crazy because they make stupid people believe they are getting a great deal. Rare coins, GOLD!!! Buy buy buy Just like those ruined Colorized $2 bills they advertise as "Two dollar bank notes are among the rarest of US currencies!" now get your colorized Yellowstone note with a GENUINE LEGAL TENDER SERIAL NUMBER!!!
Because fools buy them hand over fist. Most don't even realize they are plated. They really think they're getting a solid gold coin.
You answered your own question. They do it because they can then sell them for twice their value. And the rarity statement is absolutely true. Until they manage to plate more then fifty percent of the quarters in existence the plated ones are rarer than the non-plated ones. I agree to me the value is deminished as well. As for defacing the coinage, so what they can do that, it's perfectly legal.