I am looking at options for getting from the North to the South Island in December. I found this website selling ferry tickets: https://www.viator.com/Wellington-tours/Ferry-Services/d399-g15-c69
What's weird is that they are selling InterIsland tickets but when I go straight to https://booking.interislander.co.nz/, I see higher prices (like 50% more). I specifically compared exactly the same setting, 2 travellers, no car on 15 Dec, and while Viator gives me $85.50 InterIsland sells this for no less than $130. Also, I can only get a 50% refund with the latter (a flexible option would be $150), but Viator says I can get a full refund.
A reseller having lower price than the provider and better cancellation policy looks like a big red flag. But it's just possible that they have some weird kind of deal or special offer. Or that I just entered something somewhere very wrong. Are they legitimate?