We were experimenting with BuySellAds and found out that their backfill recommendation for AdSense is wrong and actually violates AdSense policy. For those, who are interested in running Google AdSense backfill code in BuySellAds correctly, we have created a sample implementation.
Guess it was a good thing you checked that out. Was this a problem you came across or were you looking for something in particular when you realized this? I am always interested to see what people find out of due diligence versus in an accidental way in one shape or form.
We use AdSense for a long time and when we wanted to try BSA. The problem was that BSA does not list you in their market even when your application is successful. You do have your property in BSA, but buyers can not see you in the market. Their support told us that they will ad us to the market "when they have buyers for us". This makes very little sense, but what it means is that BSA is unlikely to serve us any ads in the nearest future. This means we needed backfill for sure - backfill is what is displayed in your ad zone when BSA has nothing for you (your ad zone is not sold). Obviously, we wanted to use Google AdSense and while implementing it, we found out that BSA uses CDN to deliver backfills and this is how it started.