Is it OK to open a package that you have no intention of buying?

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I went shopping with a friend yesterday, she needed a new cover for her cell phone. We found the covers, and she promptly opened the package right there in the store to see if it fit her phone. I didn't say anything at first, even though this is something I would never do, I figured 'to each there own'. The problem, though, is that when she found out that the cover did fit, she put it back in the package, put the package back on the wall, and picked another of the same thing, just one that had not been opened. In my opinion, if you have to open something in the store, that's one thing, but if you decide to buy the product, then you at least take the one that you opened! I gave her a hard time about it, but since she works in retail herself, she said 'people do it all the time, there's nothing wrong with it.' What do you think? Is she right or wrong? What would you have done in my position? (for the record, she is an adult, so this isn't a matter of her just rebelling or something like that.)