CDKeys ethicality

vacantinthesoul​  CDKeys and other unauthorized third-party sellers do provide legitimate keys, but not all the time.  The problem is that they're willing to buy from other sources, so they can wind up selling keys that were originally stolen or otherwise fraudulently obtained, and CDKeys has no insight into the validity of any given code.  If the user ends up with a bad one, EA won't provide support because the seller isn't on the approved list, and the code isn't legitimate, after all.

Not all bad codes get caught right away, so some get cancelled after initially working.  This is less of a problem than it used to be, but judging by recent posts, it does still happen.  The point being, you can't count on your purchase working forever going forward even if the code is accepted initially.

The other point to make is that with these sites, not only are you paying less than EA is charging, but the codes will have passed through more hands on their way to you.  So a smaller pot of money is being divided among more parties, and it's possible, depending on how things played out in this particular case, that that list doesn't include EA at all.

Anyway, I would wait for EA sales, where Sims 3 and all related content (aside from SimPoints) can be 50-60% off.  Steam also offers sales and is an authorized seller.