I understand that it is considered a given that a Shadchan gets paid for the work put into making a match, regardless of when the payment should or shouldn’t be made. But I have a nagging issue about the whole thing: If two people, who are meant to be together, are never matched up by a Shadchan, isn’t it still obvious that they’ll meet some other way or at another time? Isn’t G-d in control over these things? What exactly is a Shadchan doing, aside from perhaps making them meet a little earlier, or taking some beginning awkwardness out of their relationship? I also don’t like the general idea of some random person who barely knows me trying to set me up with someone. I don’t care how “good” or “professional” they are.
Anyway, about paying them, since it’s considered a given, one should definitely pay. But I do agree with some of the posters here about stating the rate up front in order to avoid possible confusion or bad feelings.