Those who charge tuition fees can be more secure and learn skills. Masters devote themselves to teaching you and provide you with a platform for internship and study. Naturally, you should get something from your hard work, with input and output.

Those who don't charge tuition fees may use labor, and it is unknown that they use you to seek benefits for them.

So, it depends on what you think and what kind of mentality you have. What are you willing to choose and refuse? All on one person.