Herbette, from France, sells on 17 June 2018 a "Melchers" signed and dated (1900) portrait of a man, estimated at 400 to 600 Euro.
It is unclear why they haven't made the connection to Gari Melchers (1860-1932, "Gari" is short for Garibaldi!). An important American artist from the turn of the century, he also worked many years in the Netherlands, France and especially Germany.
catalogue of that exhibition we find more than 30 paintings by "Gari Melchers, Paris", including a "Männlicher Studienkopf", a study of a male head (well, there are two of those, but the other is a pastel).
Now, it is possible that someone found an unsigned turn-of-the-century painting of a man's head and added a frame, signature, and label on the back which all fit together, but that seems rather unlikely, so I guess the logical conclusion is that this is a genuine Melchers from his best period (his paintings after the first World War are less interesting in my opinion).
The value? One painting fetched nearly $1 million in 200, but most are around the $10,000 mark, and this is only a study. The estimate, up to about $1,000, may be about right (the exhibition provenance should help). But the seller and auction hosue would surely have a better chance of getting this target if they clearly advertised this for what it is, surely?