It is a bit rude, actually. If a boat's on YachtWorld it's by definition brokered, so you're paying more for it as a buyer and getting nothing of value in return, and it's already been shopped to a big audience.
Forums like this one are a good place to find a
boat that may be
for sale under the right circumstances for that seller, which may mean avoiding the hassle and cost of a
broker or a thousand tire kickers if you're selling by owner. If someone came here to post for a boat wanted ad, you can assume the person knows about YachtWorld and has already exhausted that resource.
If you don't want to see boat wanted ads then stay off the "Boats
for Sale and
Wanted" thread, for Pete's sake!