The usual mechanical causes of failures-to-extract for S&W 3rd gen's are:
Damaged/worn extractor, extractor spring or a recoil spring.
Replacing the recoil spring is an easy place to start. (Wouldn't hurt to replace mag springs at the same time on a used gun with an unknown maintenance/service history.)
Eyeballing the extractor hook is easy enough (chips or breakage).
Checking spring tension isn't easily done, though. Visual inspection requires removal of the extractor, and checking tension requires use of a force dial gauge (and the appropriate hook extension for pulling on the extractor hook, checking for weight reading at moment of deflection).
Of course, while many folks are inclined to suspect a mechanical cause of such problems, the use of handloads (worn brass, over/under-powered loads, etc), or less-than-optimal quality factory loads (over/under-powered), might sometimes be involved, too.
Condition of chamber is always good to check, as well. (Something stuck against chamber wall?)