I like that Ghost Rider starts off by saying you are better off not doing them but then goes on to say he does a lot of them. That sounds exactly like something I would say!
We do a fair amount of re-surfacing for free, well not really for free, the testimonials from those customers are like gold. We also drill into and fill air spaces, fill cracks that were not filled or cured properly the first time, etc. If we can improve the stability and cosmetics significantly we charge, otherwise we just do it because we feel bad that someone else did not do the job right. Sometimes customers will give tips for being honest and kind, sometimes not, but at the end of the day helping someone out always feels right.
We always tell the customer if we believe it has been repaired before and we are always honest about whether anything we do is going to improve the chances of the windshield not cracking out or if it is simply going to make it look a little better. In the shop it is no big deal but when you are driving 15 miles each way for a mobile job it is frustrating when you don't get paid.