poster didn't say anything of the sort. but given the situation you're constructing, i'd expect they'd buy only what's necessary and all things being equal from the one that advertised least.

Yeah, precisely. In that case I'd only buy what I need. If there are multiple sources / alternatives, I'd buy from the one that advertised the least. If they all advertised equally, I'd probably ask people I know which one they found the best and research on the best alternative.