Well, my OPINION is that if a dealer/collector
leaves a cel up that has already been sold, it's
to me saying...

"See what you missed?! Visit often!"

To me this is a good thing. It tells everyone that
this person can get good cels and there's more
to come! EX: Usagi's House, Anime Chaos, etc.
These great dealers leave their sold cels on
sometimes because you can see what they are
capable of getting and you should watch for their
updates! (Or they just haven't got the chance to 
erase them yet.) ^_^;

Personally I don't because I don't like to waste
space, and I don't want to be reminded of what I
sold. (I cry sometimes. :P )
Still, I think it's not only eye candy but also
good business sense.

As for the right to have the cel removed if you
paid for it... not really. They own the "image"
because they scanned it. If you want to get REAL
technical, the cel's image is owned by the studio.

Something to ponder for a moment. ^_^

Ke-chan