Once the seller confirms that he still wants to trade, he has 10 minutes to send you an offer. You cannot request other listings from the market once the seller confirms your trade, until the trade is completed.
If the seller doesn't send you an offer within 10 minutes, you can click the "I didn't receive an offer" button to lock the listing.
Once a listing is locked, a member from Staff will be needed to review your listing to solve the dispute before you can create or purchase listings again.
You can speed up this process by contacting Support.