Mmmm. I think you misunderstand. It sounds like you are running a mark down sale. One of the permeameters of that are you can choose Price of items in that category. Like $10-$50. Doing this would only apply the markdown percent of the price 20% to those items in that price range.
The above has nothing to do with the minimum offer price. You have to set that in each listing. You can bulk edit your listings and set that minimum if you want, rather than doing listings one by one.
A mark down sale only marks down items you specify or categorize it to. It only changes price for the period of time you specify. It does not change anything else about the listing. You have to set up the offer minimum in the listing.
@toydaze49
