We ordered something similar to a crockpot from a local store (paying for a new item). When the store delivered it, it appears that it was opened before (box wasnt sealed, and instructions were missing). If the appliance looks basically clean, is there a reason that we would have to assume that it may have been used before and then was returned (and would be a kashrus concern?)
In this instance, since it was bought from the store and meant to be sold new, plus the fact that it is only questionable if it was used, and even if so, if it was from a non-Jew using something trief. Therefore, you can assume that it is still kosher.