When the time comes look hard and look seriously. Make sure you choose what you will actually use the most often (this was a tough decision for me). The boat will be yours so only has to make you happy not others, don't let someone talk you into something you don't want and don't be in such a hurry that you settle for less than you want.
Make a list of exactly what you want out of or in a boat
:
Should store how many rods, how much gear, bait well, live well, fish box etc., how many passengers. Think hard about this list, do you want storage for a BBQ an area to sleep etc., etc., etc.
For sure sea trial the boat preferable on a less than perfect day and see if the boat broaches coming down swells. See how she rides in tough seas and what shakes loose or falls off.
Use a an inspector even if it is a small 20 foot boat as they will alert you to cracks in the transom and or other potential problems.
Remember a bad outboard can end up costing you 16k to replace. Do you want an outboard (2 or 4 stroke) or an IO (Diesel or gas) etc., etc. Make sure she will have the range you will need.
Don't overlook the electronics as they can add up quickly if you need to replace because they are outdated, will not work for you needs or do not come with the boat.
Make sure the trailer is in good shape as well and the breaks are functioning. Would suck to have a 20k dollar boat on the side of the road when it should be heading to the islands.
At 20K you can almost get into a new boat if you stay in the 20' area bare bones but then again you would be better off looking for a better make that is used or at least IMHO.
You have been around boats long enough to know. Use your best judgment, common sense and gut feelings.
LAST BUT NOT LEAST have them throw in their GPS numbers for their hot fishing spots heheehe