On a Saturday afternoon in late May, Dania Rose Colegrove stood in the shade of an oak tree, waiting for a small group of young runners to crest the hill on a dusty dirt and gravel road.

Online marketplaces helped launch the internet into the stratosphere, taking it from the domain of geeks, nerds, and academics to a mainstay in the lives of everyday people. At their pinnacle, websites like Craigslist and eBay — before the latter and similar services like Etsy starting squeezing sellers with outsized fees and confounding buyers with increasingly convoluted user interfaces bloated with unwanted features and rife with scams — offered users immensely powerful marketplaces where they could find or sell almost any item their heart desired, no matter how specialized or obscure.