I don't know if this is a good idea. In the marketplace (and in other similar exchanges) people will generally trust people who they have traded with previously. They will trust people who have done a lot of transactions with people that have traded with a lot of other people (see default trust). If you were to say that you trust "no one" then the vast majority of the trades would not be able to be facilitated because neither party would be able to "send first"
Use a multisig escrow. Past performance does not guarantee future performance. Pirateat40 was the highest rated user and always paid on time for a year up until he scammed millions. Trusting people based on the fact they have had lots of positive transactions in the past is a bad idea, that is how all of the biggest scammers pulled off their scams.