It may be sold as truth, but how important is truth to the value of the product?

Sedaris' work certainly doesn't belong with the body of political writing where individual authors tout their own grasp of the truth while contradicting the truth as endorsed by others. Truth certainly isn't a standard that is stringently adhered to in the field of nonfiction, even when it is important to what writers hope to accomplish. Even if there were an attempt to hold some sort of standard for truth, that concept is so poorly defined and so dependent on individuals' perceptions of the world around them that opportunities to discern truth from fiction without controversy would be very rare.

Take, as an example, James Watson's The Double Helix, which has been widely criticized by others involved in discovering the structure of DNA as excessively dramatizing their endeavor, focusing on personal interests and conflicts that were blown out of proportion and failing to communicate the professional nature of their endeavor. Whether Watson maliciously chose to distort actual events, or whether this is how he experienced those same events is not a question open to factual analysis; instead, as Sir Lawrence Bragg suggested, the book is best read with the understanding that it provides an account of things that happened, and therefore qualifies as non-fiction, but does so in a way that is determined by only one individual.

The consequences of accepting this approach are even less substantial in the case of Sedaris' work; the purpose here is not to inform readers of the details of events but to entertain. To that end, Sedaris is apparently very successful, and so the cost of accepting that his work might not describe events with mathematical precision is to low to entirely disregard the connection that it does hold to reality.

Certainly, there is nothing to be fooled by unless one assumes high-enough standards for human communication to run the risk of being made a fool.