I have worked in customer service basically...forever. And so I hate to be the difficult customer, however you are obviously under-informed when it comes to how things in your store are priced. I buy vitamins/supplements when you put them on sale for buy one, get one free. That is why I bought four bottles today.
You ring them up and ask me if they are on BOGO. I confirm. Then you tell me it's only giving me one of the four free. Well, obviously that's wrong. Then you tell me that it's because you have to buy two of the same item. Obviously, this is NOT the case, since I have four different items in front of you, and at least one rung up as BOGO. So... wrong. Try again. Then you tell me that the items have to be the same price. Nice try to look like you know what you're talking about. But you're wrong. Don't try and convince me, it says "of equal or lesser value" on the sign. That OBVIOUSLY means that they do not have to be the same price.
I feel bad for holding up your register, and that you had to call your manager over to figure it out. At the same time, a little bit of common sense and logic would have made you realize right away that I am right, and you are not, so I do not feel THAT bad just because you are stupid.