Heroes that often work alone don't have the luxury of getting paid. They give up a lot of their free time in order to do their duties in fighting evil and protecting the innocent. Even though Spider-Man is on the New Avengers, he can't get paid since he insists on keeping his identity a secret (we all remember how badly things went during Civil War when he revealed it to the world). Is it fair that his need for privacy and desire to protect his family and friends prevents him from earning a paycheck for doing his job? At least he has a well paying job in his civilian guise now.
If the comic world is anything like our real one, the idea of brands and logos should exist. We've often seen people wearing t-shirts or drinking out of coffee cups with the logo of a superhero. With the flashy heroes flying around saving the world, there's no doubt that people would want paraphernalia sporting their images or symbols. Who is making a profit off of all this merchandise?
== TEASER ==
What's to prevent someone else from registering a trademark before the hero can? That's actually what Rex Leech, Superboy's manager did (when he first became a hero). Superman was thought dead and being a businessman (of sorts), Rex filed a claim to make a profit off of Superboy merchandise. When Superman returned, he allowed Rex to continue selling products as long as half the profits went to charity. After all, it's not like Superman needs money since he has his salary at the Daily Planet and apparently doesn't need to show up to work (since he spent a year on New Krypton and is now walking across America).
It's also been seen in the Marvel Universe that Marvel Comics actually exist there. Some of the heroes inform the publisher of their exploits and the stories are written, most likely, without the personal side and information that we see. If the Marvel Comics in the Marvel Universe publishes comics on Spider-Man or the Punisher, do they keep all profits?
It's only fair that the heroes should earn any money being made off of who they are. For those that have secret identities, some sort of cash payment could be made. There could be some sort of test to prove who they are and a secret password or something could be set up to prevent someone with mimicry powers to come in and try to change the business terms. How the heroes would file their taxes on any merchandise profit would be a tricky area. Also, the hero would have to avoid becoming a sell out as Booster Gold had often been accused of.
If superheroes are sacrificing large portions of their lives to save others and a profit is being made, why shouldn't they get a piece of it, even if making money isn't what they set out to do. And if they don't want the money, they could always donate it to me.