Like multisided models, marketplaces are multi-actor models made up of two different segments: buyers and sellers.
Unlike multisided models where users are the riskier side and can be tackled serially before customers, in a marketplace model both the buyer and seller sides need to be tackled simultaneously.
Monetizable value in these models is typically captured as a percentage of the value of the transaction created between buyer and seller as a commission, listing fee, et cetera.
This is the most complex business model archetype because you have two customer segments (buyers and sellers) that need to be firing together.
A key pattern for success with this model is first identifying a preexisting marketplace with lots of transactional friction. If you can remove some of this friction for your early-adopter buyers and sellers, you represent a compelling value proposition that draws buyers and sellers from their existing alternative(s) to your marketplace.