Hmmmm... I vote for separate listings of items available from different sellers.
When you go to the 'Classified' section, the item available or sought is listed on the left hand side of the page along with the name of the individual posting the item.
IF piggybacking within the thread... the new, additional offering is 'lost' to those not digging through the whole thread.
Many times, after initially looking at something being offered or sought, I do not re-read the additional entries because I've already determined whether I'm interested in pursuing the item or able to help someone else with their search.
My opinion.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York