Thanks with all the replies.
With the off-season question, I only been in the hobby for about 6 months, but I have a friend been in hobby for 15 years.
He told me the card value generally drop around 20% over the offseason.
High end cards values normally less variable than low end cards.
With John Wall, its bit strange, the value actually increased a bit over the play-off. I think it's because when people watch Rose, reminds of Wall.