Just a curious doubt

So i was shopping in Lulu yesterday and I had some fruits which had to be weighed. I was waiting for my turn where the person weighs and sticks the price on the bag, and I had this question - How do they know which variety of the fruit it is just by looking into it? I mean, there are like many varieties of red apples, oranges, dates, etc! And each variety have a different price. How do they know which type of apple or orange i have in my bag? Do they memorize the name and look of the fruit or something? Also what happens if i mix 2 varieties of apple in one bag? I haven't done that, but it all just went through my mind. Thanks 🥂