I have a very simple policy regarding chargebacks. Don't give in.
I tend to take it to the highest level I can, and usually can prove my case pretty solidly. I think in just over 14 years (yikes), I've only lost a handful of chargebacks... Then again, I maintain a relationship with clients where I don't have them.
Whether I win, or lose, the chargeback user is immediately suspended and reported to fraudrecord. That kind of abuse won't be tolerated, at all.