As far as I know, it’s not customary. When I like a teacher, I’ll take more lessons than I otherwise would have — this is what tells us we’re doing a good job and we’re appreciated. I love my regular students, so your presents are your presence (lol). Sometimes longterm students will book a class and let me know that it’s a gratuity and they don’t intend to take it (make sure you work with the teacher to choose a time-slot that’s not needed for a real lesson). Alternatively, it is possible, by agreement of teacher and student, to change the price on an individual lesson. Whatever you do, make sure not to make any payments outside of the italki website.

Okay good to know. I was just wondering.

I don't think it's possible to tip the teachers. They set their rates. You pay the fee. That's all.

If so, how would one go about issuing a gratuity?

Hi! I don't think it is expected but the support team will give you correct answers if you contact them. Bye! :)