A Short History

 The first postage stamp was issued in Great Britain in 1840 and within a few years forgeries to fool collectors began to appear in great numbers.
The lack of catalogs or those that often showed images of forgeries only complicated matters.

Senf Brothers - Forgers

Forgeries were not as many think only of high value stamps, many lower values were forged often to defraud postal authorities.

The period in the early 1900's called the "stamp packet" era increased the need for stamps exponentially and forgers naturally benefitted.

Jean De Sperati - Forger

When a collector buys or inherits an "old collection", it generally contains forgeries. The age of the collection only increases the possibility of having forgeries.

There's nothing wrong with having a few fakes and forgeries in your collection, as long as you know what they really are. They can be collected in their own right, or they can be part of a reference collection for use in identifying other stamps as genuine or forged. Most serious philatelists agree that defacing or destroying classic forgeries serves no purpose. 
In many cases, forgeries from the best forgers can command some impressive values.

Francois Fournier - Forger & Reseller

Today modern postal forgeries account for $Billions in lost revenues worldwide, however they have no value and this is not a topic of interest for the purposes of this blog.