Repeated Ads in different units

[marbles88]

On one of my sites I have 3 ad units. A skyscraper, a 300x240 box, and a textlink. The skyscraper and the box frequently have the exact same ads, but in different sequences.

Isn't Google supposed to check for that?
Is there anything that I can do?
Is that a reflection of a thin set of advertisers?

[MyNewPC]

Happens on my site all the time. In the early days of AdSense, Google prohibited this but they no longer do and there is nothing we can do about it.

At least with my site, it's not an indication of too few advertisers. There are plenty.

[greatstart]

I'm using a different ad channel on each one of the ad units. It seems to help, but I still get a few repeats.

You might try using only 2 ad units instead of 3. You will also get a better eCPM as a result of it.

[MyNewPC]

I'm doing exactly what greatstart suggested and it hasn't helped me.