There is already the black discount label on Items For Sale view - would it work
on the Price Guide ?
Thinking this through I see it would be abused and clutter up the Price Guide.
People would be doing 1% bulk reductions. A threshold, say 5%, could work better
but could still be abused I suspect. Eg. 5% off when you buy the entire stock
of 12457 black 3001 bricks..