Things in Tmall supermarket are so expensive, why do some people say they are cheap?

Tmall supermarket is quite cost-effective for users who buy it for the first time, but it is not good for those who buy it later, and it is a big pit for students who are not sensitive to price. At any time, there will be activities that are over 99 minus 50, but if you are more sensitive to the price, you will find that the original products are only sold in 20 yuan in the supermarket, and 48.9 yuan when you go to Tmall supermarket, and then you also reduce 8.9 yuan with a discount. Sometimes, in order to meet the set meal, you will buy something that is not so needed. Students who feel good at math can try it, and various comparative calculations should save a few dollars. Forget it, my girlfriend, a math idiot, is just wasting money. I think Tmall Supermarket still exists because its activities are complicated. If you subtract 50 from 99, you can buy two and get one free. If you subtract 10 from 50, you can't buy two if you subtract 10, 1 ... Then in fact, its activities are much more complicated than what I said, and consumers simply don't understand. Anyway, I think Tmall supermarket will take medicine sooner or later, and you can't say it's fraud, but there's really no way. I don't understand why it is like this. It's interesting to have pits. Small profits but quick turnover? Do you have to lie like this?