It's hard to predict because a dealer has a better ability to sell for their price than any of us. For us to move the bike as individuals, we need buyers who can bring cash or arrange their own financing and don't need to trade in. Because of the financing, they WILL know the book pricing and what their banker told them he would loan on a given bike.
The dealer has a huge advantage here because they have their own financing sources, the ability to take trades and offer warranties plus they have the customer traffic.
It might seem obvious to one of US that the price is "over book" but I'd wager that *most* used-bikes sold at the dealers ARE. I'd further submit that at least HALF of those buyers had no idea the book price; they saw what they wanted and asked where to sign.
I don't say this to impugn Harley buyers, it's likely true of most markets, but especially recreational items.