>There will be no site that does not offer advertising, because advertising allows the site to determine which sellers can afford to pay more while still being profitable.
It's still possible that people exist who charge "what it's worth" rather than "what they can get". Those people can still make a fine living off of a two sided market place through flat transaction fees. Craigslist is an example that comes immediately to mind. Smart market participants are already punishing providers that maximize profit with payola, which is leading to success of new smaller niche markets - reverb.com comes to mind, or bricklink.com or alibris.com. That is not to say the market of markets is "solving" this problem - we probably want more consumer protection law - but it does show that your startement about ads is, strictly speaking, false.