Source Sans Pro for the texts
In a Sharetribe marketplace, text is displayed using, by default, the Source Sans Pro font. It is used in different styles and sizes.
This font is Adobe's first open source typeface family, was designed by Paul D. Hunt. It is a sans serif typeface intended to work well in user interfaces. You can learn more about this font here.
Helvetica as a backup
If, for some reason, Source Sans Pro couldn't be loaded, then Helvetica is the fallback font. Helvetica is one of the most famous font and even has its own Wikipedia page.
Proxima Nova Soft for the default logo and Custom Landing Pages
If you use the default logo (in the top left corner, that uses your marketplace name), that logo is displayed using the Proxima Nova Soft font.
Custom Landing Pages also use that font.
Here are more details about that font.
How to change the font in a Sharetribe marketplace
If you want to, you can change the font used using your own Custom Script. This requires some technical knowledge though. Sharetribe doesn't offer any support on how to make that change.