It's set up as a marketplace where experts can have ballpark hourly rates and clients can also offer a specific rate for a given request. Then a mutually agreed upon amount (could be zero on up through top-dollar market rates) can be negotiated. As an expert you can decide "I always want $X/hour" if you like or you can do it case-by-case. Same thing as a client, you can specify in the request an amount you are offering and let experts take it or leave it.