Heres a few links :)
http://www.tutorio.com/tutorial/pure-css-image-rollovers
http://www.edginet.org/techie/website/cssimg.html#ROLL
http://www.findmotive.com/2006/10/31/simple-css-image-rollover/
I guess it would depend upon the trouble caused, but I'd say best business practise (unless he/she is breaking Terms of Service) would be to remain polite, courteous and bend over backwards to make sure that word of mouth remains positive :)