Artful, eggzackly the way I use bidStart and Stamps2go. I would say, though, that it need not be a seller who has zillions of stamps overall. What matters, really, is that he have a good, comprehensive selection of what I want! Now if what I want is a stamp here and a stamp there from several differnt countries, yes, the one with zillions from all over the world will get my order.
But often I'm looking to fill in gaps in a single country. So if a seller has only a few hundred stamps but happens to have a pretty thorough range of, say, Portuguese Congo or French Polynesia and I have a lot of holes in those countries (in some cases I'm going to bidStart to get started on a small country I have virtually nothing from, like the two I named), he'll get my order.
But yes, I go to bidStart almost always in search of a particular stamp or particular country or type of stamp. For
ebay it's more often "Hey, what's so-and-so, one of my trusted sellers, got listed this week" or "what's newly listed in my particular areas right now."
I almost never bid in bidStart auctions anymore; almost all my purchases there are fixed priced stamps.
Of course I'm a classic WW collector and thus am often "doing" a country rather than seeking unusual, newly listed stuff in a hyperspeciality.
I buy as much or more on bidStart as on
ebay.