Generally speaking, yes. However, like buying anything online, it comes with certain risks you should consider first.
Many successful sales of Onewheels happen on internet forums including Facebook Onewheel groups and Craigslist. However, there are also a fair number of successful scams resulting in would-be riders getting conned out of a large sum of money. There are many factors that go into how to safely purchase a Onewheel from a private owner; too many to list here. We recommend you check out Jimmy Chang‘s detailed and thorough article on How to buy a used Onewheel. Something else to consider; if a deal looks too good to be true, it probably is.