I have never seen one in writing. No. Some could be verbally implied but I personally haven't dealt with that. I've always had clearly stated contracts one way or the other. Some have taken it apon themselves to break my contracts. They are few and far between though. But it can happen and it's hard to enforce unless you involve the court systems. Like Yorkierini said a while back...if you want to insure they aren't bred, spay or neuter before they leave. (or something along those lines she said, lol) If you are offering to a potential breeder then realize they could actually do it. Lay it all out on the table from day one and go from there!