Apple will exchange products purchased directly from Apple within 14 days of initial purchase. They will not exchange products obtained through third-party retailers.
Trade-in values will only represent a fraction of the corresponding as new price of the iPad - but is sometime a useful vehicle to recover some value when replacing an older model with new:
Apple Trade In - Apple
Instead of Apple trade-in, you may achieve a better value if you sell your unwanted iPad privately.
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support