Decades ago when I was selling new and used smaller sailboats my "gross profit" on the new ones was about 17%, and I often had to sell for a lot less just to compete.
After a few years I got out, having proven the old adage about making a little money in boat selling by starting out with more money, or somesuch phrasing.
Anyhoooo, at the time all the dealers that I knew were in it for the love of sailing first and money second. Sailing does that to otherwise rational people!
There are probably some
production builders and larger dealers making real money and able to afford attracting "discounting."
One major difficulty is how many buyers are preconditioned to the larger retail world of heavily-marked-up stuff advertised and sold at an everyday "discount" and do not understand that small markets like sail boat production seldom work like that at all.
Also note that in a niche market like sail boat building sometimes the "list price" is not completely logical, although most small builders usually try to keep it simple by adding up real-world labor and materials and then pricing to give them some minimal profit.
It's an odd game, on its best day.
As to saving on items added after the sale, it's common for established dealers to grant a buyer access to the dealer's Port Supply account for a short period of time after the sale closes.