Domino’s isn’t “taking advantage of you not knowing how the system works” when they plaster the deals in all caps on their homepage. They want you to use the deals, and make it very easy to use the deals.
I would think there’d be less obstinate boomerism on Lemmy, but apparently not. You have eyes, you have fingers, and presumably a brain. You could have used them, you didn’t. You paid more than you had to as a result. You now have the option to learn, and not make the same mistake again.