Does it work because you're taking advantage of a group of people who are extremely vulnerable to manipulation? People who already struggle with impulse control, who are prone to making bad financial decisions? The elderly, kids?
We have to escape this mentality that anything that makes money is valid, that the money itself is the validation of "rightness".
Some of us, just some think that maybe enterprises that prey on the vulnerable just don't deserve to be in business. Otherwise everything might as well be payday loans and online gambling. I'm not saying OP is definitely in that category, but I would encourage them to think long and hard about weather or not using dark patterns to goose their sales is really the kind of world we want to be fostering.