Shaggy, Daphne, Velma and Fred usually solve ghost-related abnormal crimes every day, with their Great Dane dog partner Scooby Doo, while traveling across the country (sometimes abroad). They don't seem to be doing any jobs. Although it's noted that some members have rich parents and/or close relatives, we cannot assume that they'll provide money for the kid long term. In the series, we see mostly the team is in their youth, (probably somewhat in their twenties). So it normally means that their parents aren't providing for them now. (common in US and Europe countries). They may need money for food supplies (a huge amount of money considering Shaggy and Scooby's eating capabilities), gas for the van, other vehicle related expenses, and other expenses including paying taxes.

I haven't seen any of them charge for catching the bad guy/ghost from their client. Most of the time they don't get a client but they themselves get caught into the trouble.

How is the team funded? How do they get the money for their expenses?

According to Scooby-Doo Behind the Scenes (released in 1998; see Wikiquote), the initial money to start out was given to them by Daphne’s dad:

Daphne: "Well, Daddy gave us the money to start off. (shows an image of the check that first financed Mystery Inc.) We didn't even have a car, so we gave our parents gas money to drive us around."

In addition, many of the different canons have shown them having jobs. (In some of these they are adults though.) From the Wikia page for Scooby-Doo:

• Junior detectives-for-hire: Contrary to the above, when the gang was in their preadolescence, they worked out of a clubhouse, calling themselves the Scooby-Doo Detective Agency, and charged a minimal fee for their services in solving the mysteries in their hometown of Coolsville. (APNSD)


• Actor: Scooby got the role of Sandy Duncan's dog, after solving the case at Mammoth Studios. (TNSDMovies: Sandy Duncan's Jekyll and Hyde)


• Carnival owner: Scooby, along with the rest of the gang, was given a share of Dick Van Dyke's carnival, after saving it from going under. (TNSDMovies: The Haunted Carnival)


• Construction worker: He, Shaggy, and Fred took questionable jobs at a construction site. (TSDS: High Rise Hair Raiser)


• Freelance journalist: Scooby, Shaggy, Scrappy, and Daphne became freelance journalists, forming the second incarnation of the Scooby-Doo Detective Agency. (TNS&SDS, TNSDMysteries)


• Gym teacher: He, Shaggy, and Scrappy were hired as gym teachers at Grimwood's Finishing School for Girls, or so they believed. (Scooby-Doo and the Ghoul School)


• Co-racecar driver. (Scooby-Doo and the Reluctant Werewolf)


• Aiport customs: He and worked in customs at an airport during the break-up of Mystery Inc., but were fired when they ate all the confiscated cheese. (Scooby-Doo On Zombie Island)


• Detective: He, Shaggy, and Scrappy worked for Shaggy's uncle Fearless Shagaford at the Fearless Detective Agency. (The Scooby & Scrappy Doo Puppy Hour)


• Additionally, Scooby assisted Shaggy when he was a paper boy, by unloading the delivered papers into his bike's basket. When the gang discovered Shaggy's boss stole his bike chain to work his counterfeiting machine, Shaggy quit, and so did Scooby. (APNSD: A Bicycle Built for Boo!)

Something else that might impact things:

Scooby Doo MAY be set in a period of economic recession.

It is never outright said in the show or by any of the creators, but there is a lot of evidence that points towards the Scooby Doo universe being in the middle of an economic recession:

(source: http://scoobyfiles.toonzone.net/monsters/index.html, as well as a number of other articles that pop up when googling "scooby doo recession")

1. Nearly every episode was set in some sort of abandoned place where there would otherwise be a lot of people: an airport, mansions, castles, a ski resort, an amusement park,... Every location looks broken down, unused and abandoned, like the economy just doesn't support the activities they encompass.


2. Nearly every criminal was motivated by monetary greed: a rare coin, a family treasure, a smuggling operation, theft for resale,... And even those that weren't motivated directly by monetary greed just wanted a job, or in one case were motivated by hatred against robots, who tend to steal jobs. There were no crimes of passion or crimes of hatred of other people, which means that most people just wanted to get money.


3. Most of the criminals had skills that could easily land them a job: several PhDs, lawyers, engineers, scientists, entrepreneurs,... People that could easily legitimately make money using their skills in legal manners,... If there were any jobs around.


4. They don't seem to make all that much money for food and other necessities. In a number of episodes, Scooby and Shaggy react very hungrily when they encounter large amounts of food, as if they don't know when they next get food. And they seem to easily be bribed by relatively small amounts of Scooby Snacks from time to time. And look at how scraggly Shaggy looks. It seems like they're struggling to get by for the most part.


5. The gang actually is around high-school age: between 15 and 17. They might look older, but their official age as given in the show bible were given as Fred and Shaggy being 17, Daphne being 16 and Velma being 15. So if these kids are of high-school age, why are they not at school? It seems like these are just a bunch of bored kids that have nothing better to do with their time than to drive around the country in search of things to do.

All of this evidence points to Scooby Doo, and especially the original 2 seasons, to be set in the middle of an economic recession. Most people with specialized skills don't have jobs, and have turned to crime in hopes of getting money. Tourism and education have gone down the drain because people don't have the money to travel or pay for education.

So they might simply not need that much money because there isn't that much to spend it on. The gang may just simply be a roaming group of high school age teenagers that are in search of anything to do.

They all have rich parents and don't travel far, so considering gas prices are low in the US, it is very plausible that they use their allowance to chip in for gas and that is all they need. Even Scooby-Doo comes from a rich dog family, and Shaggy received some big plantation as an inheritance. Only Velma is middle-class, but she worked for her parents in a museum.