Rule Number One
I'm the kind of guy who rarely cooks at home, not because I don't necessarily know how to cook (I can try), but because cooking for me is far more expensive than eating out and this is because I'm the only one at home.
So due to the fact that I mostly eat out, I have this particular food vendor that I frequent her shop to buy food. Almost every morning I would walk up to her shop, buy the exact same thing I always buy (which in most cases is usually rice and beans and then some fish for protein).
Whenever I go to her shop to buy these things, I always make sure to ask her about the prices of everything I'm buying, even if it's not my first time buying the same exact thing. This is a habit I've developed during the years and it's a habit I definitely won't be stopping anytime soon...even though there had been days where I could tell that the lady was upset due to the fact that I was asking about the prices of something I clearly bought the previous day.
But you see, I've seen multiple occasions where I've gone out with friends to certain places and they had ordered for stuff, stuff that we clearly know the price of, but after we're done consuming that thing, they begin to call other prices for us, prices that we had no idea of, but due to the fact that we already consumed that product, we have no choice but to pay for it.
This has happened to people around me far too many times (some times I had to come in and help pay the bill), that I've vowed never to be in such situation, especially when it's just me out and no one to help me. It almost happened to me one time, when a lady at a bar had tried upping the prices to some drinks that I had bought for some friends, but luckily for me, I had asked for the prices before they opened the drinks, and when I found out about the change in price, I had refused and wanted to return them until the manager overheard us and pretended like that was the new price but he was going to givs us discounts.
I found out they were trying to trick me because I had asked someone else who had also bought the same drinks how much they paid and they had mentioned the old price. The manager probably said what he said to save the waitress from embarrassment due to the fact that he found out that she had been caught in an act of trying to exploit me by illegally increasing the prices of the drinks.
This is why, irrespective of if this food vendor gets upset or not, I always keep on asking for the prices of everything I'm about to buy before I even touch that thing.