Here are a few marketplaces designs for mobile apps you may like

A Horse marketplace
A minimal design for searching horses for sale via an app

A super clean design for a sneaker marketplace
A very clean look for a sneaker marketplace app

A marketplace for luxury items
Inspiration for a luxury product marketplace, e.g. cars.

Something for service marketplaces
A modern cool design with a map for finding service professionals near you.

A fun marketplace for buying and selling farm products
Fun, green and pleasing on the eye