When it comes to people casting for you, there are some things you should consider before doing anything, including assuming anything about them. The first is that, yes, some people cast for money - practitioners providing the community a service has been around since there were any practitioners in a community setting and can be perfectly valid. Many were compensated as well, through a monetary value, trading services, or through barter, though this was not the case with every single practitioner.
You have to look at the setting in which magical, religious, or spiritual services are offered; most cases were and are someone who is more experienced in an area than the vast majority of the rest of their community. Much like you would call a plumber to fix a leaky pipe you wouldn't know how to fix yourself, you could call upon someone for their occult/etc. services. In this community, however, it is encouraged that we all seek our own paths as much of the knowledge is readily available for those who know what to look for and how to look for it. Because of this, there are few people who specialize in common practices because so many can do the same.
Even with this considered, it is still commonly accepted for people to offer readings for those that ask, though the tone is much different in people usually coming to the diviner for the reading. Not many psychics in this community actively look for people to read for unless they wish practice. Some ask for compensation whille others don't, and it's really up to each individual as to whether or not they feel that's right. We all have different ideas of morality.
If you're new to having a magical service provided for you, then it is often considered best to steer clear of those that ask for money and those that try to bolster themselves up to look better. As you get more experienced in interacting with others, as well as having a general sense of what magic is, what it means to you, and what it can or can't do in your eyes, then it will be easier to distinguish who is legitimate and who is faulty.
Some General Red Flags
People who offer help without getting to know the situation.
People who offer long lists of success stories that have little to do with what they are offering, or those that claim outlandish feats.
People offering up their email to contact them outside of the site when there's a fully functional mailbox system in place here.
Some like to avoid those asking for money, period. Personally I find if there are no other red flags and I get to know the person beyond their service and it's not the first thing I get to know about them, then I still proceed with caution.
If you're a minor, do not engage with any person who comes to you with a service, asking for money or not.
There are a lot more red flags that come along with experience and the general rule of thumb is to trust your instincts - if you doubt them, ask around for more opinions.