Please check the price and shipping price you are charging for every item. 

Prices that were set in the stores are set as a place to start and it is up to each store owner to make sure that those prices work based on your marketing plan.

Pay special attention to shipping costs especially if you are shipping internationally. International shipping prices have increased and could eat up all of your profit if you aren't careful.

With the store you can currently only set one shipping cost for an item. There is no way to set the shipping cost at one price of it is US and another if it is international. You may want to consider disabling international shipping until a future release of the software has an upgraded shipping settings section.