Trade a Plane, Barnstormers, Aircraft Controller all will give a hint to value, but airplanes listed do not mean sales.
How very true. When I was shopping for my Cardinal I was tracking about a dozen examples for sale. In some cases I called contacted the seller after the plane was sold and (among other things), asked them what the final selling price was.
None of the sellers would give me that answer.
As such, it was very difficult to find out what a plane was truly worth.
One suggestion I do have is to peruse eBay. If you click on "Advanced" Search, you can specify "Completed" or "Sold" listings. That will show you what the plane actually sold for, not what the reserve or asking price may be.
Next, take the specs of such a "sold" 150 or 152 and feed it into Vref. Hopefully, given a few examples, you'll get a consistent answer as to how far off (high, low, or right on the money) Vref may be from actual market prices.