One of the websites I administer wants to provide free advertising in the form of direct links to vendors at an event they are running. Up until now, there has been no advertising whatsoever on the site (or any of our other sites).

The site is for a for-profit business.

The idea of implicit endorsement of any vendors we advertise has been raised, which brought up the question of what we need to do, if anything, to protect ourselves from any potential problems such endorsement might create.

I know that many sites have clauses in their Terms of Service that state that (in a nutshell) they are not responsible for any problems or grievances between the visitors to the site and any vendor advertised or linked.

Are there other steps that a website typically takes when considering advertising, such as getting the advertiser to provide some sort of certification that their ad will not violate any trademarks or copyrighted material?