Let me say first off that I have no problems with people stopping by the
various ship trainers on a regular basis to see if any "new and improved"
crewmembers have arrived. I do mind people sitting on top of a trainer and
botting "list" every few minutes. This includes the possibility of sitting
right outside the room, and hopping in for a second and back out, hoping to
escape my notice.

I do check periodically who's hanging around the rooms, and I'm pleased that I
almost never spot people idling in one of the rooms, so by and large this has
not been a significant issue (although I'm also well aware that people will
probably complain loudly about not being to get all the trainers they want
upon reading this).

In recent weeks I've noticed a sharp drop in average "idle time" between when
a trainer specialist appears and is bought, from ~40-60 min to ~5 minutes, and
I've also caught one person frequently idling at the hiring zone. So, I've
given myself a new banishing option - while on the list, you may not hire any
specialist crew of any type.

This is a totally separate issue from "enough trainers for all" - I keep an
eye on how many of the trainers that spawn are bought, and periodically bump
the rate of appearance up. This is in response to the increasing number of
people buying and using ships, but don't expect it to ever reach such a level
that everyone can get all their trainers on demand.
Trainers are meant to be special, and there are other ways of improving your
ship (e.g. daria's recent post). I do have plans to allow you to "make" a
small number of trainer/unique sailors per ship, but I'm coding as best as
I've got the time to, so it probably will still be a while.

Anyway, this has rambled on long enough.
Melemkor