Today, the role of the Shadchan is, depending on your community, to suggest to the prospective match that they meet, to introduce them, to arrange their meetings, and/or to advocate / be the intermediary for their communications while they are dating.
However, in the halachic literature about Shadchanim, much of the discussion is about their brokering the financial arrangements between the two sides of the match - who will pay for what, what the dowry will be, how long the parents will support the couple, etc. In fact, the Rema (C.M. 185:10) classifies a Shadchan as a type of broker. There is no explicit mention (with which I am familiar) of the Shadchan being involved in the actual matching up of the prospective couple.
Did the old-time Shadchan serve as the one who suggested the match? Was there such a thing as a "professional" match-suggester, as we have today?