am i doing something that will get me arrested

A certain store uses a sticker (shank) that they place on sold items as a proof of purchase. They also have a sister store that sells their out of season clothing at reduced prices.Wandering around the discount store I noticed a lot of these shanks on the banks of certain price tags. So if you buy the item with the shank you can make a decent profit by taking it back to the mother sore and returning it using the shank you found at their discount store. is this illegal????

Sounds Illegal. The store is losing money and you are misrepresenting your purchase by claiming you paid more than you did. I would avoid this situation at all costs.

I believe that would be what they call both ticket switching and return fraud and yes, if caught, you can be prosecuted by the store.