Take it back
You're right that a new product shouldn't be rusty. Try taking it back and see what they say.
Bought mine with the bike and never looked inside. Now, almost 4 years later, it's mos def rusty on the outside from being sand and gravel blasted. I'm thinking of visiting my local Line-X guy to get it covered up and protected. Might even give the bottom a little more purchase on my garage floor.