The only problem I can see with locking threads is people being in-undated with PM's of the same thing saying "Will this fit my...." whilst if this was just in a thread at least that way people can read the replies and see without the need to ask again.
When I see a locked thread in the for sale section my instant reaction is that the item has already been sold so the thread has been locked.
GLWS doesn't seam too bad, I've used it a few times, never actually just posted it always put it on the end of a question or something.
I can just see it creating more hassle then is really needed of needing to repeat yourself and empty your inbox a lot?
....I totally agree, and also with stealth's post.
Also by keeping it public it keeps both buyer and seller more 'honest' and fair - Everyone can see what's going on.
"GLWS" is only okay if it's like a smiley on the end of something useful to the thread being said.
Too many PM's is a nuisance - I wish that some folks would ask me questions in public rather than by PM, though it depends on the question. I'm talking about questions which can benefit lots of people on the forum by being public.
I'm actually put off being interested in items sold only via PM.
@ DaveB:
If you're like this at 40yo what are you going to be like at 50?