An account of things heroes learn on their journeys, rumours they hear, and people they meet may be interesting not only to sages. Intelligence agencies for example.
Become an advisor for someone powerful.
If popular, some hero may even write a book about his deeds. (bleh, celebrities...
Maps of little known places are sought by smart commanders of war. (also a plot hook)
A recently failed plot about clearing a rat-infested mansion brings new uses for Alchemy and Poison-Brewing to mind. Rats, insects, all kind of vermin we kill for you.
For those with love for money through any way, Necromancers are often in need of "source material". After slaying those bandits/Orcs/Trolls/anything, sell their bodies to your black friend.
One illusionist payed in a tavern with his Art: the ugly barkeeper's wife became Pamela Anderson. Lasted for only one hour, but the barkeep didn't complain...
If you have lots of money (for a moment), lend it to others.
Rent your golem for heavy labours.
Casting locking spells on secure-to-be places. Needs much trust though.
Create traps or test the security.
Open up your own school for training in combat.