What's wrong with your English skills, sounds just like it is your first language! :)
If the person is not part of any private trackers (as many of your new members are) they have 0 experience. Somebody could also answer they've been part of private trackers for 4 years, but it is really just demonoid and where you don't even need to keep a ratio or worry about anything. However, if demonoid is their only tracker, it will be listed in their intro so you would know.
I think that the idea doesn't add much overhead to the intro process, so it would be easy to implement. It would be an interesting extra piece of information to look at when giving out your invites. But I still think if you are giving away a prized invite you can/should ask for a ratio proof showing their profile or even profile links to their oldest tracker and check up on them first.
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Wanted to add that I also noticed this on Yahoo Answers! When somebody asks what a safe and virus free site to get content from, everybody is recommending The Pirate Bay or other sites like Kick Ass Torrents!
Yet, apparently 25% to 30% of content on these sites is fake:
25% of files downloaded from The Pirate Bay are fakes
I agree that people who have 5 years experience with torrents may not have a clue about private trackers!