The best Telugu teacher I ever had didn't charge me for the first lesson, but they didn't advertise it that way. And because of this, I wanted to pay them more than what a typical lesson should cost! I think when paying for language lessons, there's a higher chance of getting better quality. But, there are also a lot of beginner tutors/teachers, and I think they can just charge a lower amount until they build up their confidence & experience with teaching. Free trials for anything aren't fun, because there's an expectation to continue paying after. Freemium models are usually better, or even showing ads. I think it helps to offer options for those who really can't afford a service, for example, one app I used gave the option of more features for more ads on the screen. I didn't use it, but it's still a cool thing to offer.