No, they don't.
I have re-bagged a few books that I bought at cons that had stickers on the bags and sometimes the stickers do leave marks on the books inside. You might only be able to see the mark if you hold the book at a certain angle or in a certain light. It also probably depends on the thickness of the bag and how tightly the books were packed in a box, and for how long, etc, etc, but it can happen.
Yes, it can. I've seen it countless times. That's why I never use stickers for anything and immediately rebag anything with one.
Sometimes the dent is extremely deep.
Without a doubt stickers will leave impressions over time depending on the way the book is stored. Even the flap of a bag could leave an impression if stored too tightly together.
This is correct. I've seen that too. (thumbs u
I purchased quite a few books a while back that all had those impressions on the b..c. from the flap being tucked in, and being compressed in a box at 200 p.s.i.