That set is showing at $399.95 (a four cent discount, they’ll have you know!) on Amazon. Any set that is still in production (well, on LEGO.com it says “we are currently making more”) and being sold online by 3rd party sellers at less than retail should raise a red flag. Or at least a yellow one.
This seller charges sales tax (5.25% in PA), and there’s something else fishy because it won’t recognize my zip code (or any of several others I tried) to calculate shipping. I didn’t find anywhere online that they could’ve gotten this set (esp. in large quantity) for less than retail price, definitely not enough below to turn a profit selling at or under MSRP… so yeah.
I’d be wary with this one. If I had to guess, I’d say “purchased with stolen CC, then flipped (via drop shipping) to unsuspecting buyer.” Saw some of that with the Fire Brigade a couple years ago…