Your post sounds all too familiar.  However, I refuse to grind down the teeth on chains that have been run in the dirt or otherwise used and abused making dust instead of chips for far too long.  I reset the drags and make their chain cut aggressive enough to wear the teeth back to a proportionate length relative to the heighth of the drags, and then explain to the owner what's going on.  He'll get the use of his chain that way, but he's going to have to be careful with chain set that aggressively.

I don't mind tounching up the rakers/drags, it's pretty easy and very fast on my grinder, not much of a problem except that $#%* low kickback, safety chain -- what a PITA.  I usually charge extra for those just for the pure frustration endured working on them. 

I appreciate all the replies here.  I think I might consider raising my prices for a few "customers" and just leaving it as is for the rest.