Certain games lend themselves to a 'gambling' meta-game with an in-game economy. But when that meta-game taints multiplayer competition with "power ups" for pay, it's bad.
We're accustomed to a natural progressions of unlockables as we play the game, that's fair. In CoD you reach level 52 to unlock one of the best assault rifles in the game. So, a level 52 in a lobby with a bunch of level 10s has a distinct, published and known, quantified advantage. Level and Prestiges translate to time in-game.
If a game allows the substitution of money for time in an in-game economy then it should also be quantified on the player's icon in any lobby. Next to a money icon a sum should denote how much real-world money they've spent on in-game economy features.
However, this runs completely counter to the way these in-game features are setup, you're not supposed to know how much you've spent. For those who do spend money on in-game economies its a scarlet letter of shame.
When researching this article I found an Angry Birds forum (maybe it was a reddit), I was interested in learning the relationship between casual gamers and in-game economies that demand real-world money.
One post in the Angry Birds forum asked players to quantify how much money they spent. The original poster said, with some distain, that he spent almost a thousand dollars.
Apparently he was the only one to ever spend money, nearly everyone (hanging out on an Angry Birds forum, remember) posted that they spent $0. There was definitely an ethic of shame associated with putting real-world money into the game and a lot of pride in saying you gamed the system through some act of in-game baddassery, which I do not comprehend because I've never played Angry Birds, it happened to be the only "pay-to-play" games I know the name of so I looked for it.
Nobody wants to admit how much they spend, and the game system itself is designed to make it seem like a low-cost, incidental investment in a $5 token pack, that you will be liable to do multiple times over time and lose track of how much you've spent.