If you are getting traffic from geo-locations that are not set in your ad campaign, then the point is in matching IP addresses.
TrafficStars uses the Digital Envoy database. This database contains IP ranges and country identification, and it's constantly updated. It's, in fact, among the most precise databases available on the market.
Check which database is used by the software/platform you are using to detect the country's IP. The use of different databases will explain the discrepancy between statistics.