Every once in a while, a Nagel anomaly comes along and this coming week, one's coming up for auction. This time, it's a framed, preliminary pencil sketch. The starting bid for this piece is $400, which isn't outrageous. The question is whether the piece is legit.
Of course, it's a pencil sketch, so you wouldn't expect it to be signed. But then again, it's a pencil sketch on tracing paper, which is just about the easiest way to fake anything. The other issue is whether a pencil sketch has any value beyond its aesthetic. This is where things get sketchy. I recall one auction (this story told here before) where an unsigned acetate (one of the "stencils" used in serigraphy) sold for US$10,000.
My own views on pencil/preliminary sketches is that they have a charm of their own, but the only ones I buy are actually signed or have some other legitimate provenance.
As usual, caveat emptor.