If you're using the database and are not advanced it will cycle through certain stores looking for things to buy. Some stores simply will not have anything worth trying to buy in that timeframe, such as the tiki-tack.
If you're using lists, make sure that you actually have items listed in there. It will be refreshing aimlessly if you don't.
Sometimes you can go an hour or two without even seeing anything missed. This is just bad luck and more than likely a result of there not being enough people using the site currently to force a restock of that shop.
By what i know , i'm not using any list. accidently while i was cleaning my desktop i deleted it and after i empty the bin. how can i use it again?