30 years ago I was repping a line of small sailboats for a builder nowadays long out of the business.
My "gross profit" was about 17%. I was told ( no proof) that big dealers for the major lines of production boats were getting about 20% or maybe more.
Of course there's doing what you gotta do to make a deal... and sometimes I settled for less.
Unlike those big boys, though, I had no flooring costs. Bank Flooring really kills the dealers in lean times.