As someone who follows the used boat market fairly closely I'll point out a few things I've learned about buying and selling boats...
"No time wasters!"
Nothing makes me want to avoid looking at a boat for sale than an ad that has the "No Time Wasters" text somewhere within the ad. In my experience people only use that phrase when folks come, look at the boat, and then leave without buying. A process that, when habitual, tells me there is something wrong with the boat on some level. Could be the condition, a too high price, or just the fact that the seller gets up the potential buyers nose.
As someone who's traveled far to look at a boat that is in not as advertised condition more times than I can count and confronted with sulky sellers who act insulted when you ask to turn on the engine or let you look in the bilge and never even bothered to do something about a weeks worth of dirty dishes moldering in the sink it's my time that's being wasted.
Sellers with poor math skills.
There's a certain situation you'll find in a lot of ads where the current owner brags about all the money he's poured into the boat but the math just doesn't make sense. A recent ad for a boat that caught my eye was that the owner had paid $15K for the boat, put in another $25K, and was selling the boat for $12.5K now, anyone with basic math skills can do that math in about a second and it just does not make sense. Either the owner is trying scam you or he/she is an idiot. Either way it's best to be very very careful as there is almost always something extremely nasty laying in wait on such a boat.
Clutter and dirt.
If I want to sell a boat the easiest way to do it is to have a clean, clutter free boat for potential buyers to look at. Even better is to take decent photos that are date stamped showing a clean uncluttered vessel with visible horizontal surfaces to attract potential buyers to the boat.
Knowing what a boat is worth.
It's just as important for the buyer and seller to know what the general value of a boat is. For instance, since I have a CAL 34 I'm pretty in tune with what the boat is actually worth and know that you can find a good condition CAL 34 for around $15K and for other boats I always do a bit of research to come up with a sort of average boat price. So, when confronted with someone selling a CAL 34 for $37K and told by a seller that old CALS sell for up to $50K I know that's some serious bullshit and best avoided. A little homework is a big help whether you're selling or a buying a boat.
Dominance games
Sadly, there are a lot of real assholes selling boats. Most assholes I come across have serious self-image issues and feel the need to play mind games. I've also noticed that a lot of the assholes who sell boats know very little about the boat they're selling and fill their knowledge void with a heavy helping of BS. A good way of keeping the BS in check is to do your homework about the boat (Sailboatdata.com is easy) So when the seller tells you the CAL 34 was designed by Bill Tripp you know you'll need hip boots.
Anyway, obviously none of us like to waste time and energy in the pursuit of selling or buying boats