Google adsense more than 3 ads on single page

Question

how can some sites have more than 3 ad units on single page?

I saw this on: http://1sale.com/electronics/

There are 4 ads, is this all adsense, and if not, what is this? How can this be possible when google allows only 3 per page?

Answer 1

Short answer:

It's not Google Adsense, so there are other rules for ad placing.

Long answer:

If you inspect the specific elements, you can see that these blocks are not AdSense unit (the divs don't contain the class 'adsbygoogle').

I also don't recommend implementing more than 3 ads because your page will look cluttered (probably more users will click on ads when the page looks nice and not full with ads). That's also why Google only allows 3 ad units.