How to check person's doubles?
Go to menu "Collectors" and find person.
There is the choise "Doubles" in hover menu (it appears on right side for each row when you move mouse pointer over row)

How to check and order coins from person's doubles list?
1) Go to your trades menu "My trades"
2) In "Trades list" you will see your current trades.
3) Clik on number in column "OA"(ordered amount). You will navigate to "Your's wants list"
4) Push button "Add". You will navigate to "Item's list: Your partner, items for trade"
5) Now choose country and push "Search". You will get list of coins he have for trade.
There are column "Order" with checkboxies on right. Check the coins you are interested in
and then push button "Order" at the top. It will save your order in data base.
Do the same for other countries. If for country is more then one page of items then you will see page indexies at the bottom.
When you will check out one page, push button "Order" before go to next page.