Why is someone elses web site address showing up on an ad on yahoo for my business?

[Jake]

Sorry it's not perfectly clear whether you actually meant a paid Tahoo Advertisement, or one of their other listings...

I do see the discrepancy in the free Yahoo Local listing,
http://local.yahoo.com/info-22218728-sou...rbor%2C+WA

There is probably an online form for reporting errors, which might be a foul up of their automated system, or the result of some sport of hijacking.

On the Google version you can "claim" your local listing in order to enhance and modify it, it someone else managed to claim to be the operator they would have the power to directly edit the information, (at least Google local confirms business ownership with a mailed postcard or phone call)