Benign comments there are fine. We don't want a stale place. But any kind of extraneous pricing or other things, by other than the poster, is not permitted. Of course fraud and/or lies can be called out. Always shoot me, or another moderator, a PM if there is something which you think crosses the line or needs to be discussed.
Examples- You got a great deal on that card, Why are you asking so much for it?
NOT permitted
That is a great looking card you have there. I used to own one and loved it. Good luck with the sale.
Permitted.
And what is a thread without a card?