I am with Jaan who said
"Not in my opinion at all. You can do what you want with your website as Google can do what they want with theirs."

If Google wishes to read our pages so that it can use this information to run its own business, then it should simply learn to read them properly. I think the whole topic of, 'is this ethical' is totally an unwise way of looking at things.

For myself, I will continue to not to put no follow tags on any link on my sites. I do not care If it screws up google's results. Google results are nothing to do with me. . In fact if Google wanted me to adjust my site in any way to assist their search engine. . They should simply do what everyone else does. send me an email.

something like
Dear Tubby, can you give me a price to place no follow tags on an insurance ad you have placed at classic cars, classified adverts and car parts - get back to me Goog..

Dear Goog, That's a bit of a problem mate. I have committed myself for the next 12 months . I can email you when the ad is about to expire and we can work something out that will help you get the result you need.

I do not work for Google. . .

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