Your broker is likely using soldboats.com to ascertain the REPORTED sale prices of those boats. I used the same several years ago for my own research, and came up with roughly the same numbers, something like 90% of asking was the sale price on average (my data was on smaller boats).
I prefer to search yachtworld and craigslist, but sometimes use boattrader.com. In print, I like Soundings and California & Pacific Northwest Yachts.
Jeff