Bucket shop usually refers to a particular type of fraudulent business.
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.
References
Bucket shop Wikipedia(Text) CC BY-SA