When you create a listing you can choose to promote it. A promoted listing sits in one of the first few slots of its category and carries a star in the corner, so shoppers can tell it was promoted.
You are only charged if it sells while the promotion is running. If the promotion ends and the item hasn't sold, you pay nothing at all — there's no up-front cost and no invoice. When it does sell, the promotion fee is taken out of your payout for that sale, alongside the usual commission.
A promotion runs for a fixed window (two weeks by default — you'll see the exact length and price when you choose it). Slots rotate every 15 minutes, and different shoppers see different promoted listings, so a busy category still gives everyone a turn near the top rather than the same few items sitting there all day.
For rentals, one promotion covers the whole window. If the item is rented out and comes back while the promotion is still running, it keeps its slot — you're charged once, not once per booking.
Promoted slots never override a search or a sort. If you've searched for something, or sorted by price, you see exactly what you asked for.