I'll give this one a try too . . . I hope I don't insult anyone, by explaining it in simplistic terms.
When you trade with anyone in the game, the trade screen pops up. On the left side is stuff you can offer (this includes gold, potions, armor, weapons, etc. . . ). On the right side, it shows what the shop keeper has (not necessarily a shop keeper, due to the fact you can trade with just about anyone in the game).
The trade screen opens up to Trade, as a default. I say this so I can explain two other functions of the trade window. You can have some traders (people you trade with), identify items for you, and/or repair them. There are more people who will identify and trade, than there are those that will do all three (trade, identify, and repair). George is one of the few that I can think of, that will do all three functions.
At any rate, you begin to trade with someone, and the trade window pops up. You look on the right side of the screen, and see, oh, let's say, a sword you want to buy. You click on the sword, and it pops into the right side, of the middle window. This is what you have selected as being the active item(s) for the current trade.
In order to get that item, you have to give the trader, an item, or items, of greater or equal value. This would include trading him another sword, gold, or tons of other stuff. The important thing is to remember the greater than or equal value.
Look at the top of the trade screen, and it will show your current trade value (which is the gold value of all the items you have put up to trade), it will also show the current trade value of the trader (it'll tell you how much the sword costs). Once the values are balanced, or your side is greater, you can click the accept button.
The trade window will close, and the sword will pop into your backpack, under the weapons tab.
That's how you trade. The process for repairing and identifying objects, is very similar.
If you weren't talking about that, perhaps you came to George, after he had been visited by the vampire, for the second time (I won't spoil it for those of you who don't know what I mean).
EL