This is a great idea, and in fact, I've implemented the marketplace here: https://bitcoinerfreelance.com

The goal of the site is to be a freelance marketplace where bitcoiners can buy and sell services using sats.

Trust is a very, very, very challenging problem and ive spent over 1 year working on it. the best that I can come up with a custodial model + buyer and seller reviews.

Currently the site is p2p payments, and just sellers have reviews so far. I will definitely have to implement reviews for buyers. The site started out as custodial, and i have since switched it to p2p payments, but I am looking to add back at least the option for payment custody.

There is always a risk of fraud in any marketplace - its inescapable, without the marketplace operator personally inspecting every order as its fulfilled. Therefore some element of trust is always needed. Hopefully, reviews will proved to be a good general guide for which sellers and buyers are reputable.