That's true, finding something 'unique' is difficult considering there's 6.6 billion people milling about, most with ideas about one thing or another. Maybe this is why I'm no entrepreneur, but the service the main players provide is pretty damn good, quick delivery, availibility of stock, prices and returns policy. Something hard to beat, and equally hard to market if you do.
That being said, online shops do have low(er) initial setup costs and overheads, if you're keen and think you can make it, go for it!