A VFNH single of the 10c brown lilac King Edward VII from the 1903-1908 King Edward Issue with engravers slip in the lower left corner, where the vertical frameline extends right into the margin. It is not shown on Trimble's re-entries website, and this is the first time I have seen it. The gum appears to be NH, but I thought I could see a very faint shadow of a hinge mark at the bottom. But I am not 100% sure, even after looking at the stamp 3 times.
Unitrade values this at $2,800 for NH and $800 for hinged. It does not list the engraver's slip, but this should also be worth a premium. So, the value should lie somewhare between these two amounts. I'm thinking $1,200 is a reasonable value. The stamp offered here grades 80 as follows:
