Gamanit,
Teenage babysitters. Few will tell you over the phone how much they charge,
My wife always asks a potential babysitter what her rate is beforehand, and will offer a rate if the babysitter responds that she doesn’t have one. Similarly, my plumber will give me a range before starting work; “It looks like you’ll need this, which costs around $350, but if I get in there and find that such and such is broken, we’ll need to replace the whole thing and that will run up to $850…” My auto mechanic always calls with an estimate before beginning work on my car. I can look up each dental procedure my dentist recommends to figure out its cost beforehand as well.
Despite the fact that a shadchan deserves payment as much as a babysitter, plumber, mechanic, and dentist, for some reason, it seems culturally more acceptable for the latter professions to state rates beforehand. In other words, a plumber would never have to start a CR thread asking for a polite way to request money instead of a gift for services rendered. Maybe this is what should change. If there is a significant problem with shadchanim not being paid appropriately, then perhaps community rabbis can be asked to highlight the halacha when addressing their communities, or be sure to mention the common rate when speaking to a family making a wedding.