It's the cost of doing business. You are lucky. At least your not a physical retailer who has to ship the merchandise back via UPS to the manufacture for refurbishment just because it's been opened. Your cost of delivery is extremely low, so just focus on creating better and better content and don't obsess over chargebacks here and there.
I would use all that analytical time to worry about leaked logins, which in my opinion are more dangerous.
Google Alerts can be helpful in detecting your domain name with the term "password" and "passwords". Be creative. Phantom Frog is another great solution, which allows the user in question to reset their password after being locked out of your site which reduces customer service time.
Chargebacks are probably 50 percent illicit users and 50 percent ignorant users with computer problems or couldn't get your videos to play. My suggestion is to tell users to download VLC media player and
Microsoft Security Essentials (anti virus) which are both free. These alone may significantly reduce chargebacks. Further more, I would also have a help desk style help center with knowledge base functionality. Use other peoples YouTube tutorials to help your customers. Think smart and out of the box.