This is not a REAL broker, just one or two blokes in a back bedroom with a computer, no address, not even the plot that a second-hand car sales firm has, so it was an insult to Arthur Daley to compare them.
They use a cheapo web hosting company in the US and freebie e-mail addressing with no listed company premises. You'll never get satisfaction from people like that; they would ignore any invoice or complaint. The only recourse is to get their e-mail address on some spam listing services. Anyone who uses an outfit like that to buy or sell a boat is crazy.