--SNIP for brevity- I heard of this case where the guy gave another person CPR after they collapsed from heart attack and accidently broke a rib. The person lived and sued the guy for breaking the rib
Folks have tried that, however almost all states have good smaritan laws these days, and you are protected. Providing you have CPR training.
Most courts, if not the plantiffs, realize that the person needing CPR was dying. Broken rib is a small price to pay.
BTW I'd go with Thorsen or Mechanics Choice. Available at Wally World or local discount parts houses. Both have lifetime warranty against breakage, so if the neighbor brings it back busted, you can get a replacement.
-alex