But today, we'll see an ad in a Marvel comic that encourages you to sell... Marvel comics!
Encouraging you to buy a set of 12 different comics for the price of 8 (two dollars), Spider-Man says "You can order one set or many - and sell them to your friends at full cover price with you keeping the profits!"
"That's right, greedy one. You can get 12 of Marvels (sic) greatest - before they hit the stands - for only $2.00!"
As far as I know Marvel hadn't yet started direct mail subscriptions at this point (which also sold you comics at a discount), so this is probably a precursor to that, but it's amusing to see Marvel angle it as yet another money-making opportunity, even going as far as encouraging you to be greedy!
Of course, by that Marvel knows there's almost no way you'd be able to sell ALL of the comics, since you only get one of each of the popular comics, leaving you with lower-level titles that nobody could care to buy from you (Where Monsters Dwell/Two-Gun Kid, Werewolf By Night), and especially not at the same price as they could buy crisp from the newspaper stands (the only benefit being that presumably you'd get the books a little before they hit retailers).
Maybe if you were able to buy multiple copies of hot titles, or at least pick and choose what 12 issues you could buy, you'd have a decent shot at making money, but clearly Marvel was doing this to expand readership of their less popular books.
Appeared in Amazing Spider-Man #137, October 1974.