Selling links is no more unethical than shooting a gun. The issue is what you are pointing the weapon at.

If you are trying to deceive people, then link selling is unethical. If you are trying to attract the largest market of qualified buyers, then link selling is ethical.

Google only changes its methods when a particular technique is dominated by unethical practices. Regretably every change affects some ethical users, but its just one of those things in life that good people have to deal with.

A suggestion is all is to stop being so judgemental . . . there's nothing in the bible about link selling. In general, in a free economy, each individual should look after his own best interest . . . but remember, collapsing a good system by weight of poor practices is in non ones interest.