And some people won't. Others might leave a tip. But those who do pay usually pay more.
Free work is also a risk in time. An hour of unpaid work means missed paid opportunities. You never what type of customer you're going to get.
The other option is to charge a premium for all your work, setting high expectations for something unique and excellent. No pay, no play.
The tip jar model may get you customers in the beginning, certainly more to spread the word for you, but price is a heavy reflection on quality which is scarce.
Match your work and payment model to your skill set. You'll learn a lot on the value of your services.