The store will need to at least double the cost to make a decent profit, unless you are selling on consignment which means they pay you when it sells and can return it to you if it doesn't sell quickly. In that case, you negotiate the cost with the owner. Be sure to keep very good business records, and pay proper tax, as the IRS is watching you

they will tell you what their rate of commission is not you telling them they all vary so ask before you give them anything to sell

they dont give me any figure, so whats the ideal percentage for them