Just my two cents:
If an individual, or his/her mother, goes to a shadchan and asks that person to make a shidduch, then that is a business transaction and the shadchan should get paid after the completion of a successful arrangement. I have never heard of anyone paying for someones “best efforts”, only for a “successful effort”
However, my experience (yes, I am in the “Parsha” and dating, and I deal with these individuals on a constant basis)is that a lot of the amateur shadchanim (I use that lightly because I believe all Shadchanim, even the “professional” ones, are amateurs) are just yenta’s. I never asked any of my parents friends/relatives/complete strangers to set me up with individuals who are completely unfamiliar even to them. In most cases, it turns out to be a waste of mine, and the girls, time.
Yes, it is a great mitzvah to set someone up. And yes, I am grateful that these individuals are looking out for my well-being and want to see me married. However, for me to pay them because they want to do me a favor, I totally and emphatically disagree. When I do get married, I plan on showing my “hakoras hatov” to the individual who set me up by doing whatever I believe is necessary, not what others think.