If it is their trademark and their products you are selling there is no way out. Your only option is to talk to them again, say you'll give the domain but you would like to continue promoting their product with a different domain name, 301 redirect the whole site keeping the same link structure and content . more often than not the new site ranks just as well as the old one. on a side note naming them in this thread might not have been the smartest thing to do
