"Often you'll see trades of a single share where the brokerage...

"Often you'll see trades of a single share where the brokerage costs more than the stock. The computer is sussing out prices, forcing you to pay more - or get less if you're selling - than what your online broker's screen says."

"If you're not watching the market all day, you can put in an order for 10,000 shares and get just two, which we would never buy if that's what was on offer,'' Abernethy says.Having inadvertently paid brokerage on a solitary share, you can hardly turn around and sell it, because you'd be out of pocket a second time.''You end up paying more to get a decent parcel,'' Abernethy says.

From: How the robots are robbing you

https://www.smh.com.au/money/investing/share-wars-how-the-robots-are-robbing-you-20120825-24t4t.html