How to profit from an online marketplace that I will develop?

I understand that most online marketplaces take cuts/commissions per transaction. Such as Upwork, etc.

But what about marketplaces that dont? How do they make money? What are their sources of income? Such as Craigslist, Carousell, etc.

I am planning to build an online marketplace for a niche market encouraging them to sell X items/products. But these items will only give them a small profit margin so me, as the owner of the marketplace, taking cuts per transaction might seem greedy or unfair to them. Which i do not want.

What are other revenue streams when owning an online marketplace?