That is one way to do it, anyone coming through the link you provide for the ad will be credited to your own affiliate account for easy tracking.
Other options are to provide a specific discount code with the ad, you can see which purchases included that discount in your transaction logs.
Another way to track sales coming in from a specific location is to use a slightly customized cart/buy now button. You can add in an extra variable that will be tracked from an order, see the section on passing a variable for a full order here:
That would allow you to set up multiple sales pages and see which sales are coming in from which page, for example if you code in the custom variable "SALE1" into the buttons on a particular page, then all the sales that result from those buttons will include "SALE1" in your transaction logs.