There are many different reward cards and most pay between 1% to 5% back. These cards could still be costing you money though. This is because people generally spend more when paying with credit cards than paying with cash. The most often quoted percentages I see are from 12-18% but I couldn’t find the actual study these figures are based on. It does make sense to me though that people in general probably spend more when using credit cards and the percentage is probably higher than what they would receive back from a reward card.
That being said just because it is true for people in general doesn’t mean it is true for you. When using your reward card you just need to be sure that you aren’t spending more than you would otherwise. I occasionally spend money with my credit card that I know I wouldn’t have spent otherwise because I didn’t have any cash with me. This doesn’t mean I’m spending more money overall though because otherwise I probably would have just made the purchase later and if I didn’t have a credit card I would be carrying more cash with me to spend. I keep my spending quite low overall and don’t feel that using credit cards increases my spending. If I make an excessive purchase using my credit card it will probably be offset by reduced spending somewhere else. I’m confident that my reward cards actually reward me. If you’re using reward cards you should make sure the same is true for you.