Most search sites, with exceptions such as MSN and Ask Jeeves, clearly separate regular search results from the “sponsored links“ that advertisers buy on a pay-per-click basis. But at Yahoo!, which is in the midst of a technology and marketing overhaul, executives plan to start publishing paid search results alongside unpaid results as early as today, with no way for users to tell the difference, as the New York Times, the Wall Street Journal (subscribers only), and Search Engine Watch all report. Yahoo! says a site’s ranking in search results will still depend on its quality, not whether it was sponsored. But critics, including Google co-founder Larry Page, say the practice opens up the possibility that advertisers will begin to influence search rankings, undermining users’ trust. (Last month, Yahoo! announced that it was going to start using its own search technology on its site instead of Google’s.)