The point of the article is simple and one I subscribe to, analyze the contract but don't let the contract price "drive" the value opinion.
A fraudulent contract is an extreme example, but the same reality exists across the board; parties are under no obligation to arrive at a price that is "market value". Analyze a sales contract, consider it, but don't shape the appraisal around meeting a SC price and problem solved.
I personally think the author's assertion that 95% of appraisers appraise to contract price is high though his view may reflect his experience in commercial. In residential, quite often we see OMV above or below a SC price and especially when below, the SC price is negotiated down to the MV opinion.