Use the store's return policy. (Pro tip.)
This is how you can try reselling without tying up your own cash.
Before you buy, verify that the exact item can be returned. It's often listed on the receipt. Clearance return policies can be different. Keep the receipt, packaging, and item in brand new condition.
List the item right away. If it sells, complete the sale. Take the profit. If it doesn't sell, return it before the return deadline. (Understand?)
What if you use a credit card?
You can put the purchase on a credit card and try to sell it before the bill is due. That can mean no cash leaves your bank account while you try to sell the item. (Your upfront cost is your time rather than money.)
Note: The item isn't technically free. You'll still owe the credit card balance if it doesn't sell or if you don't follow the return policy. Only do this if you can pay the full balance without the sale.