Well, they can read well enough to navigate the site and click the ads...
Unless you are talking about Sponsered Links bolding the sponsored link thing, it's not gonna make much more difference the "ads by google".
You know, the web these days is totally INUNDATED with ads. Ads are a part of just about every website on the web. It does not take long at all for the average person to get "tricked" a time or two before the become very aware of what is or is not an ad. I know 8 year olds that can instantly tell you what is an ad an whats not.
Anyway, it seems google knows this too and made the accidental click "easier" to happen by introducing "link units". Those things really look like a menu bar...
I remember the first time I used them, got a huge jump in revenue for a day or two, till all my readers realized it was ads. I pulled most of em because of that.
But the point being, if readers can quickly determine a "link unit" is an ad, how much more so for a google block that already says "Ads by Google?".
I really think you are getting the feeling that your readers are "dim" like I said earlier, when in fact they really aren't. Just ask anyone in your family while sitting at a computer, "what on this page is an ad and what is not". Most people today know the difference almost instantly IMHO.