If you return and they want you to fill out an incident report then make sure in the comments you write, "I deny the damage" or "The damage was already there" and write very little beyond that. Whatever you do, do not write, "I was unaware" or "I didn't see it" or anything similar to that. Do NOT bring up the damage to the instant return rep - if they bring it up then talk about it but do not bring it to their attention.