I have a 2014 21EC. They're a great little boat. I'll skip the items already mentioned. They're good advice.
Be sure to look at all the hoses and see if any are rubbing or chafing. When I got my 21 it had just over 130 hours and there were already several spots where hoses running over sharp edges were beginning to chafe. It's not a deal killer by any means and easily fixed by fastening anti chafe material on the trouble spots. I use old pieces of inner tube cut with scissors, trimmed to an agreeable looking shape and fastend with tie-wraps.
Pay particular attention to the heater hoses where they run under the cabin floor. A dental mirror and a good flashlight help see the bad spots.
The fuel hoses should be inspected closely. Make sure the clamps are tight and, again, look for rubbing and chafing. Mine needed quite a few spots taken care of but it's not a major chore.
Check the bilge pump. Pull the pump fuse first so it doesn't come on accidently while you're working on it. In a 21 everything goes to the bilge...dog hair, fish scales, pieces of fishing line and anything else small enough to flow through the deck screens. Pull the motor portion of the pump and check for any foreign matter in the pump base and for things wound around the motor shaft.
Look at the boat in good light. Dings in the hull sometimes don't show up well if the boat is inside. A few scrapes and scratches are to be expected but cracks, obvious repairs or recently repainted spots are a caution flag.
Check all the railings, they should be firmly affixed with no slop. A lot of people tie their fenders to the railing and over time if they're placed wrong they can stress the attachment points. Again, look for dings, scrape marks, or signs of recent replacement. Same thing with cleats and chocks. Make sure they're bedded firmly
In the cabin, look inside all the cabinets. Look for signs of water ingress or stains from boat keeping supplies stored there. Check the refrigerator. In the cabinet next to the refrig reach around behind the unit and check for mold or things that have gone adrift from that cabinet. I found a couple of small tools and some pieces of electrical wire in the space behind the refrig.
Pull the bunk cushions and check for mold. While you have them up check the compartments under them for cracks and signs of water ingress. Check the bow-thruster, it should be firm and not wabbling around in it's mount. Pull the cover plate for the anchor gear locker and check for water. It's supposed to drain from an outlet on the outside starboard bow but it doesn't always empty completely.
I'm sure other 21 owners will chime in with more ideas. Good luck with your purchase.
