In Bereishis (24:3) the posuk tells us that Avraham asked Eliezer to go find a wife for Yitzchok. We know that since Eliezer was a slave and was not paid for his efforts. The common practice is that shadchan in today’s day and age is paid for consummating a shiduch.
The makor for paying a shadchan is found in Bava Metziya (87b) where the gemara says that a person has to pay an agent when he brokers a deal. The gemara says if the measuring cup breaks in the process, the agent loses the money and he is stuck with the bill for these goods. Rashi explains the reason for the agent being left with the bill is because it is as if the agent buys it from person A and sells it to person B. As long as the deal is not completed, the item in question is in the hands of the agent and he therefore takes the loss. Tosfos argues with this position and brings down in the name of the Rivam that the agent will only be responsible if the agent was negligent in the process of measuring. He would otherwise not be responsible. We see two opinions in the halacha of brokering/being an agent. Rashi and Rambam are of opinion that the agent is the one buying from the seller and subsequently selling it to the buyer, hence he gets paid. Tosfos and the Rosh are of the opinion that the agent does not actually sell or buy the product, but rather gets paid for the service of getting the buyer and seller together for the deal.
The rishonim that compare a shadchan to an agent would only be according to Tosfos and the Rosh since the shadchan is doing a service of brokering the shidduch. In contrast, according to Rashi and Rambam, since there is no actual sale, one cannot compare a shadchan to an agent.
The Gra (87) brings down the shita of the Maharam that shadchanus is comparable to a person who goes into his friend’s field and plants there without being asked. The owner of the field is responsible to pay what the going rate is to have his field planted and he is considered an agent. We see two reasons for the position of this Gra. First, that he is considered a “yored lesoch sadeh chaveiro” (a person planting someone else’s field without permission). In addition, he is compared to an agent brokering a deal. We could explain that the two reasons are dependent upon whether the shadchan went and made the shidduch without being asked by the parents. The shadchan then would be compared to going into someone’s field without permission. However, in the case where the shadchan was asked by the parents to make a shidduch, then the shadchan would be considered an agent.
The difference between being paid as an agent and being paid as a yored lesoch sadeh chaveiro would be if there would be a problem of “Bal talin” (which is withholding wages from a person). If the shadchan is considered an agent, then he or she is working under the employment of the parents and the parents would have to pay on time, whether it is at the vort or by the time of wedding. If the shadchan is considered a yored in someone else’s field, then the parents would not have a chiyuv to pay on time since the halacha is that the person whose field was planted without his permission needs to pay, but does not need to pay on time since the person who did the work is not considered an employee. In either case, there is no question that the shadchan has to be paid for carrying out a shidduch.
May we all be zocheh to marry off all our children and grandchildren!