A product can be unbelievably crappy as long as it solves a real pain point. If your product makes or saves people money, if it saves them an arduous chore, if it gets them laid, then your product can be actively hostile to the user and still succeed. There's nothing "delightful" about the vast majority of consumer products or services.
It's when your benefits are less clear that interface becomes important. Invantory falls firmly into this latter category - their own homepage blurb essentially describes them as "a nicer Craigslist". Offering a nicer version of a commodity is potentially very lucrative, as Apple and Starbucks shareholders will testify, but it's inherently more difficult to bootstrap. The incumbent players have enough resources to crush you like a bug, so you're gambling that they're too dumb or too slow. That's a big gamble, certainly a bigger one than I'd be prepared to take on a product that's hugely dependent on network effects.