Vanderkindere, from Belgium, sells on 29 May 2018 a, "Attributed to Cornelis Visscher" drawing of an artist, "Portrait de Antoine Van Dyck" (?), estimated at 600 to 800 Euro.
The drawing, which was exhibited in Dordrecht in 1968, is definitely not a portrait of Van Dyck, who was a self-confident dandy, not the slightly hunched man shown here.
It is a copy after a work by Van Dyck though, his portrait of Hendrick Steenwyck (Hendrik van Steenwijk II, 1580-1640), painter of church interiors. The drawing is good, nothing spectacular though, and whether such a copy is by Visscher or someone else is very hard to tell. But in any case you aren't buying an unknown portrait of Van Dyck, nor an original invention, so the estimate is perhaps a bit high here.