Oomis, Shadchanim who do this as a profession, even part time, have been around for a long time. I’m sure you don’t get upset when a nurse gets paid, or anyone else in the helping professions. When a Rebbe, nurse or a PT, or for that matter a sanitation worker and a gardner, do work for you, do you get angry that you have to pay them?
If someone reds you a shiduch, or clears off your lawn, and says cheerfully, “no charge”, that’s a very nice thing. But I personally don’t work for free in my profession, and it’s very surprising to me that people expect Shadchan work to be for free, except for “hakaras hatov”. I agree that hakoras hatov is important, and I have given chocolate platters to nurses, holiday tips to postal workers, a platter of cake for someone who did yard work for me, and a beautiful note with a giftcard to my child’s therapist. In all cases, the individuals get paid for their work; in the latter two examples, paid by me. The money I pay my child’s therapist is payment for services rendered; the generous gift and note are demonstrations of hakoras hatov.