Those models coexist very nicely. Percentage margins don't matter. Companies are valued not on their percentage margins, but on how many dollars they actually make, and a multiple of that. Auction pricing is most useful when it's hard to assess a fair value. So that means either that the thing you're selling is unique, or maybe it's not unique, but its value fluctuates rapidly.
Stock prices are sort of like that.
For most things, fixed prices are more efficient. The reason is that you don't have to negotiate. You don't want to negotiate the price of simple things you buy every day. I believe this is a large market, and there is room for two players to have critical mass. So it's not that somebody has to lose for us to win.