Sellers list items and they will put in a dollar figures just like a regular auction/sell.Once an item has been won or sold,the buyer will then transfer the bitcoin amount which is equivalent to the sellers asking price into the bitcoin wallet that the seller will provide after the item has been sold.
If you have found some ad which you want to visit later or contact seller later, etc. you can mark it as Favorite and it will be save to the list of your favorite ads which you can access from your profile dashboard.
If you feel that the ad is breaking some rules, you can report it directly from ad page by clicking on the Report button and writing detail reason. Ad will remain active until administrator checks it out.