I've seen many "methods" tossed about but this is a new one on me. There are cities where home values have decreased back to when the home seller purchased, even 10 years ago. But most are in the 1999 range in western Oakland County. Your area might be different.
Two suggestions. First, assuming your friends are listing their homes through a real estate professional. They could request an updated CMA from their agent. Perhaps they could also request to review all homes that have sold since the day they listed. I had a home in Dearborn Hgts that was vinyl sided without a basement. Every home that sold, was brick exterior with a basement. This may be the case with some of your friends. If so, they will have to either change their home to what is selling, or discount their price to make their home more attractive. My seller still has his home for sale. It appraised at 118,000 when he listed for 120,000. 2 agents later and a continuous declining market, the home is at 90,000. With a quick look, there are many homes in Royal Oak with large differences in their original asking price and sold price during the past 90 days.
Alternately, your friends should contact a local appraiser and request a not for refinance appraisal of their home. The cost will be around 300.00 but during negotiations, their home will already be listed "below the appraised value".
The good thing about owning a home for 10 years, if they didn't refinance several times, is that there should be enough equity to allow your friends to still come away with money after the sale.