Affiliate networks (the shadier they are, the more likely they will), because they are weird and load third party tracking beacons in transitional pages and want to make extra sure that the beacons (who also can redirect multiple times) have been loaded. To add to the fun, they're also adding random new tracking domains (to avoid being blocked, I assume), so you can't even say whether you expect some domain to be transitional or final to increase your confidence in what you measure.
You're right though, looking for elements is a pretty good way if you know the page you're checking. If you're going in blind, you can still look for things they probably have (e.g. <nav>, <header>, <section> etc), but I haven't found any that are reliably on a "real" page and reliably not on a redirect page.