In the world of gaming, as in life, you get what you pay for.

There used to be one way most people bought video games: They spent, say, $60, and the whole experience was theirs. As mobile games have taken over the industry, though, customers have become accustomed to the so-called freemium model. That means they pay nothing to download and play the game. If they get hooked, though, and want to increase a character’s power or jump to the next level, they will have to spend 99 cents here, 99 cents there.

But the freemium model is encountering some resistance. Regulators here and overseas are taking a closer look at whether some free games mislead consumers about the true costs of playing them and whether vulnerable players, like children, might be duped into spending money.

In January, in a deal with the Federal Trade Commission, Apple agreed to refund at least $32 million to consumers whose children made in-game purchases without their permission. Amazon is resisting a similar settlement with the F.T.C. involving its tablets. And the European Commission has held a series of meetings with Google, Apple and game makers to discuss concerns about free games. The commission expects to reveal the results of those discussions this month.

Some longtime players and game developers also worry that the freemium model is ruining the culture of gaming by nickel-and-diming players and making video games feel like slot machines.