Much like fraud prevention is the "hard" part in a payment processor, reputation systems are one half* of the "hard" part in this kind of marketplaces, and very especially for this kind of tradesman services (*the other is getting both sides to use it).

I've seen several people try to start services like "Handy" and fail due to this.

One big problem is that the best tradespeople already have work, and don't need lead generation services.