I can agree. I knew a guy on the inside where he had a gal who would get people's cards since she worked at a Pizza Hut - and she would wear a tape recorder and would have the orderer repeat their card information (so that way she can use it later on). But mind you this must've taken close to a year or so's worth of practice/trial/error in order to create a system like that (and I've said to the guy who knew this Woman that it's better to use a Voice Recording Application on her Cell Phone but honestly the way she's doing it seems to be effective).
Point is - is that - the OP here is right: Social Engineering is a Art and a Skill that needs to be tested, refined, and tuned to the specific situation that the Social Engineering is being applied to. Much like OpSec (though the only difference is that OpSec is just inherent Discipline that can be built up, but surely also this discipline could apply to Social Engineering).