I stumbled upon this eBay listing. Asking more than a million dollars for a DC cover on a Marvel interior, and you can't see the interior because it's slabbed! I think I still have a Charlton comic with a wrong cover, but it was an error within the same company. I guess it's worth less than a million.
Generally speaking, misprints or other printer errors don't increase the value of comics the way a mis-stamp would with a coin. the most common error I have seen is a double cover (I own three of them myself). A DC cover on a Marvel interior is unusual, certainly, but still an error at the printers and $1 million is pie-in-the-sky wishful thinking.
Several months ago, my wife ordered a $40 jacket for me from an online company based in New Jersey whose fulfillment center was in China. The company sent the wrong item and the company ignored multiple e-mails sent to their customer service. then a friend suggested reporting it through PayPal. We did so and the correct item was sent within 24 hours.
Wonderful Crazy Walmart Commercial with Classic Movie Cars