I agree with Ken. I've always found V-ref to be more like an insurance replacement cost than a sales price for the planes I've looked at and purchased. TAP is closer, but I still find inconsistencies. There are so many after market options; they just can't all be on there. Also, people keep looking at extra stuff and adding to the price; at some point, all the extra stuff doesn't matter. Market conditions are always changing.
I know some guys that have found these more accurate of some basic planes. When you get into things like A-36 Bonanzas and Barons with lots of extras; these services are just a beginning point.
Best,
Dave