All plastic boats use UV inhibitors, but it is like sunscreen - only slows the damage.
Technically being in the sun wouldn't be warrantable. Hopefully he is saying that there hasn't been anyone who has complained of issues, not just that no one has collected on a warranty.
That all said, I suspect 18 months isn't too much. Especially a shop in the north east.
If the guy really is up front - make sure you also ask if the boat is a first quality boat, not a second. Some dealers have been known to buy seconds (also known as blems) and sell at a discount. Seconds likely are fine, just have something that blemishes the look. But they are of a lower value.
Classic Freestanding Rack
PFD's (Life Jackets)
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