The advertisement says buy 3 get free 1. If you buy six, how many will you get? What do you think is the correct understanding?

If the advertisement says buy 3 get 2 free 1, buy 6 get 2 free.

If the merchant doesn't specify a gift, send one. Then, the correct understanding is to buy 3 for free 1, buy 6 for 2, and buy 9 for 3.

However, if the merchant specifically indicates a gift, etc. Then you can only get 1 if you buy 6, and 1 if you buy 9.

6 is twice as much as 3, so you get 3 1, and 3 is twice as much as a gift, so you get 2 if you buy 6. Push it back from the inside, 3 buy 9, 4 buy 12, 5 buy 15.

If you are worried that the store can't keep its promise, you can keep the advertising page.