A puppy broker is someone who sells a puppy to someone else that is going to re-sell that puppy.  Usually the buyer is a pet store or someone operating an Internet Website where you can buy puppies.  A broker may also be a breeder.

If you are the person buying that puppy you have no idea where that puppy came from.  Are the parents of that puppy kept in a cage all the time?  Do you want to support someone that keeps their dogs caged 24 hours / 365 days a year? 

Have a look at this website for more information about puppy brokers: www.prisonersofgreed.org/Broker.html