Fair market value is what a willing buyer pays to a willing seller.
Boats are not cars. Cars are necessities and sell in high volume. Their value is not so dependent on economic conditions. Cars are "fungible" and generally have fewer variations in value as boats do.
For most buyers, a boat is a luxury item. There is no need to buy one. It's value is much more elastic and depends upon economic conditions.
There are several factors to consider:
1. Supply is much greater than demand. Sailing is a dying sport/hobby/activity; there are fewer and fewer participants in the market. Buyer demand has fallen. The heyday was in the 70s and 80s, when supply was plentiful. Boats have lasted longer than anyone ever expected. There has been only incremental functional improvements in recreational sailboats in the last 50 years. There are now many more boats that can supply the functional enjoyment of sailing than there are potential buyers.
2. Fewer folks can afford to own a keelboat due to the economic recession. Discretionary income has fallen. Few are willing to shoulder the ongoing expenses associated with keelboat ownership: slip rental, maintenance, and operating expenses.
3. Most boats are barely used. Walk down the docks of any marina, any day of the week. The majority of boats are rarely, if ever used.
4. There is a lack of accurate market information due to low volume and a lack of any centralized accurate sales price informatin. Boats take a long time to sell. Many owners do not need to sell. Owners are hesitant to fully comprehend the concept of market value; they believe their boat is worth a certain amount, regardless of market conditions. Some owners do not accept the idea that they will never recover the money they have spent on improving their vessels. Contrary to broker bullshizzle, a boat is not an "investment" - boats are depreciating property with high ongoing expenses.
Your best bet is to educate yourself, be skeptical of all the marketing B.S., become aware of the supply and what sellers are willing to sell for. You should become your own market expert, and not rely on someone who will make money off your ignorance.
There are some motivated sellers out there who are going through financial distress, divorces, business failures, etc. Those are the ones you want to buy from. Look for well-maintained boats whose owners recently improved with new sails, new inboard, new electronics and other costly "improvements", not knowing that there financials circumstances would take a downturn.