A Rag, a Bone and a Hank of Hair by Jonathan Gash
 

Likeable, roguish Lovejoy is an antiques dealer with a reputation as a ‘divvy’, a person who has an uncanny ability to recognize valuable items as well as distinguishing the fake from the real.  In this twenty-first Lovejoy mystery, he investigates a dangerous case involving phony gemstones, comes to the aid of a former paramour who is now a bag lady, and faces a formidable thug named Dieter Gluck.