The term is used as a pejorative colloquialism to refer to different kinds of businesses, indicating that the speaker believes it is a fraud or scam. In this sense it might be used as a name for stock market, unregulated credit default swaps, or for heraldry scams.
In heraldry, bucket shop refers to a business working with heraldic fraud. A similar meaning is used on the stock market, where bucket shop is a defined term under the criminal law of many states in the United States that make it a crime to operate a bucket shop, see bucket shop (stock market).
The term is also used of airline ticket consolidators, though in this case there is no implication of fraud.