Love Ranch / Dead Ringer (Arthur Lyons) 1977
A while ago I bought a cheap 2nd hand pocket book, about a private detective called Jacob Asch. He is called by a BOXING promotor to help out CARLOS REALONGA, a South American HEAVYWEIGHT, whose career is on the skids.
He has been receiving threatening phone calls and Susan Mezzano, his MANAGER and MISTRESS, thinks her HUSBAND is responsible.
Two weeks later ASCH is called to Reno, to prevent R. tearing her husband apart, too late he's been shot at MOONFIRE RANCH, a fancy BROTHEL owned by her husband...
Doesn't that ring a bell? ;)
I guess Arthur based it on the same story, to say the least!