It looks like mold which isn't a great problem by itself. But it is also an indication of neglect. I would check the whole boat for possible issues, buy or borrow a moisture meter and determine how the cored (most likely) decks are. I hope the price is very low as the owner didn't exactly prep it for sale.
Let us know the results.
Here's a link to the purchase and use of a moisture meter by MaineSail:
Understanding the Moisture Meter / Electrophysics CT-33 Photo Gallery by Compass Marine at pbase.com
Living aboard in Victoria Harbour
Last edited by mitiempo; 03-06-2011 at 12:31 PM.