The vendor manager that Paige mentions is quite probably me!  (Argent)  And yes, these situations are EXTREMELY tricky and I do everything possible to protect both the abstractor and myself.

USE DISCLAIMERS.  There's nothing wrong with doing back-title if you need the work and they are willing to pay for your hands-on experience, but just do up a general disclaimer and include it with the work.  Something to the effect that "....this work product includes ONLY the chain of title for subject property and no other documents have been searched.  It is dependent on the accuracy of the work provided with the order."  Just CYA

I run a lot of counties myself and they're all on line.  If someone wants me to get behind a certain date, I insist that they give me everything they already have and throw in that disclaimer.  It doesn't include easements, restrictions, ROW....nothin' beyond the chain of title if that's what they're asking for.  If they want me to check for easements, I will do it WITHIN THE TIMEFRAME OF MY SEARCH.  As long as you're careful to include wording that protects you -- and you charge two arms and a leg -- you should be ok if you choose to go that route.  (Vendor managers such as myself do not hold it against you if you say "no"!  Totally understand.)