Fool the Toff by John Creasey (Hodder & Stoughton, 1954)

 

Was "Love's Matrimonial Agency" a racket shop?  Jane Abbott met her husband there and he vanished--her money with him.  The Toff went to see Miss Love and found a most remarkable woman.  Then there was Jeremiah Matt, an equally remarkable man.  In fact the Toff met many new acquaintances and one of them made a fool of him.  Others... died.

This blurb is taken from the half-title page, as the back cover is filled with an advertisement:

 

Every once in a while I stumble across one of these on a secondhand bookstall.

As for the Toff--as the title of this book says, he is indeed fooled!  In the end, all the mysteries contained therein are  solved by his "man", Jolly--which is not what you expect of a story with a crime-fighting gentleman hero!