It all depends on what the 2nd is. It is a great price for it, as long as there isn't some glaring defect. Honestly I didn't look at the ad, but if the scales are where the problem is there are aftermarket scales for the 550. I have the 560 and I love it. Even though it is a big knife it is my EDC.
I've bought KAI blemish stuff, and other than the XXXX marked on the blade, I wouldn't have know it was a second. Keep in mind though, they are not covered under the factory warranty