I didn't read the entire post but I do have an 
idea I'd like to share.

Perhaps allowing access to one 
individual "sales" page / section on each of the 
gallery sites.  You can sell a maximum of 12 
cels at a time and the total image file size 
will be limited to xxxkb.

It would be some work on your part, but there 
will be no ambiguity on selling.  This system 
would put a cap on bandwidth usage and also not 
allow image hosting for Ebay, etc.

Anyway, just a suggestion.  I can very much 
understand the need to sell some cels every now 
and then and even "emergency" sales.  I've done 
things like that from my personal gallery plenty 
of times.  Even a few cases where I just got the 
cel in the main and ended up selling it.

Reguardless; good job on Rubberslug.  ;)