By which I mean, people who strategically position themselves so as to acquire money/service/free stuff at the expense of another? I don't mean extortion (that's too strong a word for what I need). Basically, someone who is a sucker for free/paid for things and capitalises on the opportunity. Is there a word for it?
Scrooge would be a good term for this, after the protagonist Ebenezer Scrooge in Charles Dickens' A Christmas Carol, who was initially only interested in acquiring money at the expense of all those around him.
You could call this kind of person a freeloader or free rider, which is someone who will happily take free things without perhaps paying their fair share. The Yiddish word schnorrer can also be used for a sponger.
All these terms carry somewhat negative overtones.