Selling an item both online & in a physical store

[frozenropes-glendora]

I recently started selling sporting equipment on ebay that our physical store needs to get rid of. The one dilemma I have is what if someone walks into our store and purchases a glove or bat we are selling on ebay and we accidentally sell that same item online, or vice versa? How do we resolve an issue like that so we don't accidentally sell the same item twice? Thanks in advance.