Interesting read here on a case re Louis Vuitton trying to sue Google in France re people buying their trademark via AdWords – French Connection: Google’s AdWords Clipped by Louis Vuitton : Legal Bytes
Re your situation – It is hard as I can see the operators point of view initially when they see this activity but at the same time you are making an effort not to buy their trademark/brand as well so its not you being agressive purposely buying their brand in Google….Problem as Dom says is that its an affiliate deal and the last thing you want is the time, effort and money involved if they hold you to ransome