Find out what model year it is... 2006 was the last year this model was offered for sale outside of like Japan iirc. The newer the model, the more value/appeal it has. Offhand seems like a pretty good deal for a "like new" Dahon "P8" in general?
Here's the Dahon archive links:
http://www.dahon.com/archive/2004/heliosp8.htm
http://www.dahon.com/archive/2005/heliosp8.htm
http://www.dahon.com/archive/2006/intl/heliosp8.htm
Some of the most obvious differences seem to be between the handleposts (compare 2004 to 2005/2006) and the forks (compare 2006 to 2005/2004)... the actual componentry seemed to vary a little even on a given years model so that may not be quite as conclusive.
cheers