Startup Idea : Scoring professsional/services based on trust

Hello, I am from Brazil and here we have problems, for example, when we want to find a babysitter. What we actually do, is going to mouth-to-mouth, asking friends if they know someone. If our friends trust in that professional(the babysitter for example), it is probably that I will trust too. The most important trait of a professional here in Brazil is the trust. So i would like to make a network, that can connect professionals/services and score each of them based on a trust score. So if you hired a babbysitter and you are connected with me, then for me, this babysitter will have a high trust score. It is important to show, that this babysitter doest have a global trust score (like for example restaurants in Trip Advisor). It has a score relative too me. So it is very difficul to fraud the score mechanism. Does anyone know a similar service? feedback sugestions are welcome!