Difficulty is one of the major motivational pull of video games, and thus many games use Dynamic Difficulty Adjustment (DDA) systems to improve the game experience. This paper describes our research investigating the influence of DDA systems on player's confidence, evaluated using an in-game bet system. Our hypothesis is that DDA systems may lead players to overconfidence, revealed by an overestimation of their success chances when betting. This boost of confidence may be a part of the positive impact of DDA systems on the quality of game experience. We explain our method to evaluate player's confidence and implement it into three games related to logical, motor and sensory difficulties. We describe two experimental conditions where difficulty is either randomly chosen or adapted using a DDA algorithm. Results show how DDA systems can lead players to high level of overconfidence.