There is a 30 day return policy on optics and electronics sold in the bargain cave is what they told me, anyway, my dad and I picked up an elite 5x dsi unit for $183 all that was wrong was that it was missing a $30 mounting bracket.
I hope you received that 30 day return policy in writing. Other wise you will need to depend on the manufacturer for any warranty and I'm not sure that is available on used equipment, which is what a returned or store display is.
When I looked at fish finders last August it clearly stated on the price tag that the items were sold "as-is". I asked one of the floor assistants if that meant it could not be returned if it did not work or was missing pieces. He told me that it meant the sale was final when I made the purchase and I could not return it.
I also found I could buy the item online for less than their "discounted' bargain cave price, which was 25% off their normal price. On the items I checked, their prices were 10%-25% higher than the manufacturer suggested price for the item.
You will probably be fortunate and not have a problem with your unit.