The advice in the kayak academy's guide is spot-on as far as get some skills before buying a boat. A few weeks ago I worked as a safety boater for the nw paddling fest and watched many people demo boats over the weekend and the large majority didn't have the skills to differentiate one boat from another. The standard test paddle was out from the beach in a straight line, make a very large turn by paddling on one side and paddle back. This doesn't really tell you much in protected water except for cockpit fit. You really want to be able to get the boat up on edge and perform various steering and bracing strokes to properly test out a boat otherwise you end up with a bathtub with lots of primary stability and little room for growth.
Incredibly good advice, Nick. I thank you.