I think it's kind of cyclical, or perhaps even random. Sometimes several seem to hit Ebay at the same time and it is consequently a buyer's market. Then at other times there is maybe just one but several buyers are suddenly looking at the same time; thus a seller's market. I think the same thing can be said of the older Series I basses and the preamps. Most of the other models are traded less frequently and price swings aren't as noticeable. For instance, while it's not uncommon to see three Epics or three Series I basses on Ebay at the same time, it's very unlikely that three used four string Rogues would suddenly show up.
