Yahoo! is reportedly bid jamming, the process of bidding slightly under a competitor, to ensure they pay top dollar for a keyword, their own advertisers, according to this DigitalPoint Forums thread. The member reported that Yahoo! came in and started bidding 45p (Pence) for a phrase he had a bid on for 50p, the next bid was 20p, so he was only paying 21p to Yahoo! Search Marketing.
Let me clarify what I think is happening. Yahoo! Finance is a completely separate division from Yahoo! Search Marketing. Yahoo! Finance, as well as Yahoo! Real Estate and so on, are all huge online advertisers. I am 99% sure they run on separate budgets and have very little to do with each other, outside of being under the same company name. Keep in mind, Yahoo! Search Marketing was once Overture, it was then bought by Yahoo!
Forum discussion at DigitalPoint Forums.
Update: YahooSarah, official Yahoo! rep, replied with what I thought was the case.
Yahoo! Finance is an advertiser just like each of you and gets no preferential treatment from Yahoo! Search Marketing. I reached out to our friends at Yahoo! Finance in the UK to get to the bottom of this, and here's what I've learned:
Yahoo! Finance uses a third-party agency to manage their search marketing campaigns and bid on keywords to drive traffic to their site. They do pay for each of their bids (no discounts) and their agency absolutely does not use bid jamming techniques.
I hope this eases your concerns.