+1
if you are concerned about getting money you think is owed you, drawing up a negotiated contract is absolutely vital. setting an advance or a % of profits are both standard practices in ANY contractual agreement. then, if the artist feels he or she has been treated unfairly, he or she can take the label to small claims court. the court can then decide whether the artist or the label is wasting its time.
if you don't negotiate payment up front, you really can't expect much.