Certainly, chit-chat isn't a good idea in the BST. Ungentlemanly comments are also not a good idea; there's enough snark in this world already.
While there is something to be said for the "send a friendly PM" on "pricing mistake" issues, there is no guarantee that the seller will act upon a PM that a puck of Tabac isn't worth $30 and reduce his price, and even if he does turn out to be willing to take some advice, there's no guarantee that a n00b won't stumble on his as-yet-unedited thread and think "Tabac only $30 ... that's good, right? YGPM!!"
As for clarifying questions ... well, you can do it by PM or post ... posts have the added benefit of being public, so the answers are there for others to read too, so the seller has to post the answer once rather than PM'ing the answer a bunch of times.
As long as people don't post "welcome" on a "FS: one puck Tabac" thread ...
Originally Posted by Go West Young Man
Be there or be square. Only I can do both!
"My lord, I will use them according to their desert."
"God's bodykins, man, much better: use every man
after his desert, and who should 'scape whipping?"
Veteran of the Great Irisch Moos Campaign of 2008-09