If you can believe it, Travelzoo is over 20 years old. Yes, we're talking about going back to the days of dial up, when ICQ was a thing, and when Netscape was my default browser.
Travelzoo has a team of sales people that go out scouring the internet for offers to place onto their list of deals.
Travelzoo makes money by negotiating deals with travel brands and operators when they refer business to them.
There's something called affiliate marketing and this is when a website refers you to another site. This is tracked through cookies or unique URL parameters.
In some cases Travelzoo doesn't have any partnership through the above 2 revenue models and is literally listing them as just good content to have on their website.