It's entirely a matter of how the user is introduced to spending money in the game. Trading card games require an initial purchase - most people purchasing the

It's entirely a matter of how the user is introduced to spending money in the game. Trading card games require an initial purchase - most people purchasing them are aware of what they're getting themselves into. You know there are lots of rare cards that you'll never see, and you're fine with that when you buy your deck(s). For one thing, this filters out a lot of people who would gripe about having to pay. But also, if you play enough to really need the best cards, usually you've accumulated enough cards that you can trade with people to make any deck you want. This places a sort of spending cap on the game, after which you can compete with the best players in the world - which can be a pleasant surprise to players who haven't thought that far ahead. Modern free-to-play games start out free, then surprise users with ways to spend money in the middle of the game. As you play on, even if you do pay, you discover that there is no limit to the amount you can spend - and you see that there will always be better, more powerful users who have spent more than you. Lots of users become bitter about this once they've invested some amount of time (and/or money) in the game world.