Games that let you buy better gear or allow you to make better items then everyone else at a faster rate and then makes the game largely unbalanced even for people who have skill in the game without paying.

The sad proof that gaming is in its most dead and soul-less state so far.

Several games nowadays have the option to pay real money to enhance the experience of the player, often frustrating him unless he pays up.

Good ways to milk players of the money they thought they wouldn't spend in the game include: energy bars that reduce the time he can devote to his game, huge timers that need to be reduced for the player to be able to continue his journey, better gear to deal with players that don't want to pay, and, the most common one, the existence of a currency in the game that can't be earned without your credit card.

Pay-to-win is sadly increasing everywhere, from small games on Kongregate to medium-sized browser games such as Epic Duel, to the larger games where you need to pay to unlock certain features, such as Injustice and Mortal Kombat.

Being a noob who cant get his/her own skills, so they pay real money that skilled players would rather not waste to get an unfair advantage that should not be there

Any game policy where specific content needed to win is locked behind pay walls. Forcing people to pay, in order to access said content. While none can gain access to the content though other in game methods (combat, trading, etc)

Paying real life currency to beat players who are inherently better than you in any game.

The sad truth of the free-to-play business model.

Pay To Win AKA P2W. when you are paying for advantage which normal players don't have access to unless they either pay too or will have to grind very long (weeks and months).