Games like to make it easy to accidentally spend premium currency
. They sometimes do this by making the purchase button big and easy to push. Additionally, it may not be immediately obvious that pushing the button spends your premium currency, and once you push it, there is often no confirmation screen and no ability to undo or refund the purchase. One accidental stray tap of the screen can irreversibly spend your money.
Sometimes games may go even further and introduce a popup button right where you normally tap to play the game. For example, there may be a blue button in the lower right corner that you normally press to start a level when you have enough energy to do so. But if you have run out of energy that blue button may turn into a green button that spends premium currency to refresh your energy and start the level. By placing this button where your muscle memory has conditioned you to tap, the game can trick you into wasting your money on items you didn't intend to purchase.
Another tactic used is the "Status Quo" or "Bad Default" effect. This is when the most expensive option is selected by default, or when you must opt-out instead of opt-in to purchasing something. By making the option to spend more money the default option, some people will accidentally spend more than they wanted to. In effect, the game is trying to sneak more expensive items into your shopping basket. Without an option to easily refund the purchase, players are often stuck having spent too much.
Spending more than you wanted to can can cause a snowball effect. If you have spent money on the game, you may feel that you have to "get your money's worth" by playing the game a lot. This in turn gets you more invested
in the game and more likely to spend money again.