in a single word "yup" in the land of startups. marketing is key here, if there were no customers, there'd be no use for marketing, hence no money to spend. to wit, see Uber/Lyft recent public IPOs (the former is soon to be), companies that lose money by the truck loads (to the tune of a billion) yet investors still want to own the companies' shares.
Amazon did the same for years and years before they finally turned a profit.
Poshmark is advertising the subways in NYC, that costs a pretty penny in marketing. they have a different tactic than Tradesy who is spending marketing dollars on coupons, but same difference and it's all in the name of marketing.