It would be misleading if the ad attempted to fool users that they were about to click through to the site they were looking for using the trademarked name of the intended site. Searching for "Honda" and clicking on a link to Honda.com that redirected to another site is very shady. However, all ad units in Google search results are marked as such and I would say at this point 99% of the population knows the difference between an ad and a genuine result. Buying a competitor's name as a keyword gets you exposure to people looking for options and i dont see anything wrong with it assuming you are not impersonating someone else's brand. I can think of a certain billboard right here in LA that advertises an organic market and is placed directly above the Whole Foods on Santa Monica and Fairfax. Whole Foods might not be happy about it, but it is clever ad placement.