When researching your items identify all the information on your documents such as signatures, advertisers, content, etc., this will better help you to determine the actual value. Condition - Depending on the age of the items try to collect pieces which have no visible defects such as tears, creases, etc, the older the document the more lenient you can be. Cost - Do not spend more than your wallet can afford. Content - The content of a document can increase the value in some cases. As an example, a letter written by a soldier during the Civil War talking about a daily life and how he misses home may not be worth as much as one written about a battle that took place.
Content is the key.