Rider vs. Owner; What about commission on the sale?

The next generation of riders is changing the way they work from being employed to self-employment. The reason? When it comes to trading horses, these riders often get a bonus themselves. But what about a horse which was in training with a rider but is sold several months after already leaving the rider's stables? As a rider, do you claim commission? And is there a legal basis to turn at, for as well the owner as the rider?