Recently, there are often different free training courses such as yoga and painting on WeChat. What's the problem?

Nothing fishy, just a way to expand new customers.

Advertise through a circle of friends, attract potential prospective customers with free gimmicks (if you don't have hobbies such as yoga and painting, you won't pay attention at all, so you will generally pay attention to and consult interested customers), and give a certain amount of free/audition classes to prospective customers. If the target customer attends the free/trial course, there is a great possibility of concluding a transaction in the future.