You need to dynamically generate the link to the merchant, using a scripting language such as php.
For some of my pages I store the visitor's referrer info in a text file, along with a unique reference (the current time), and use this unique reference as the SID code. So when I get a sale I can see the time in the SID column in the transaction report, and look it up in my text file to find the referer info. I do this to judge the effectiveness of different PPC keywords.
But if you just want to find out where someone's from, you'll presumably use their IP address, which you could use as the SID code to avoid having to store anything in a separate file (can't do this with the referrer because it's too long to use as a SID).
So if it was a CJ link you'd make the link as normal, add the &SID= bit, then in PHP add the following code:
Code:
<?
echo $REMOTE_ADDR;
?>
Simple as that.
Then when you look at the sales in the transaction report the visitor's IP address should appear as the SID. You can then do a look up to find out where the visitor is from.
I'm sure with a bit of work it would be possible to write a script to find out what the country is, and use the country as the SID. But that would involve proper programming rather than the one line of code above.
Obviously this would ony work if you have access to php, and your web page has a php enabled extension.