I tried to make a screenshot but it didn't work.
Have a look at the trade window. You see your side + items and the trader side.
On your side is a small balance scale icon
(upper left side). If you click on this you pay with the money you have. If you wish to trade goods against goods, you click on an item on your side and it goes into the trading bar on your side.
The same goes for the trader's side = his items and if he has enough money, the balance scale on his side is paying you the money your item is worth.
= you accept
= you close and leave this deal unaccomplished.
Other icons, you click on and activate:
= identify, the items you want to identify on your side have a blue description underneath AND you have to pay in money
= repair, the item you want to repair has a red description, you have to pay in money.
= back to trading mode
If these icons are not highlighted it means, this trader can't identify/repair.
If the trader does not have enough money, you can identify/repair items first, then go back to trading = maybe he has enough money now for your goods?
And welcome to the forum, Nntp