Interesting, to me at least.

"For example, if the user want's to look for the keyword 'shoes', there will be three ways to search: Find all products that have the keyword shoes, find all suppliers that make shoes or find any open auctions that are offering shoes.

I also have to factor in that there might be more selectors in the future. Not many but 1 more, maybe 2.
So now my question is, what do you think would be most usable for my site visitors to select a search method? Tabs, Radio Buttons, a dropdown list?"

Examples of the various designs proposed and some good discussion.