I have a trade partner who will be using some of our content on their site. What's the best way to prevent any duplicate content issues? Their plan is to attribute the content to us using rel=author tagging. Would this be sufficient or should I request that they do something else too? Thanks

I'm about to block off all URLs that have a query string using robots.txt. They're mostly URLs with coremetrics tags and other referrer info. I figured that search engines don't need to see these as they're always better off with the original URL. Might there be any downside to this that I need to consider? Appreciate your help / experiences on this one. Thanks Jenni

Due to an error, some of my pages now have two canonical tags on them. One is correct and the other goes to a nonsense URL (404 page). I know I should ideally remove the incorrect ones, but it's a big manual job. Are they doing any harm? Can I just leave them there and let Google figure it out? The correct ones are higher up in the code. Will this make a difference? Any help appreciated.