A good friend would NOT ask you to do it for free or want to “use” you, but would come to you because they trust you to do it right and not to overcharge them. So there is nothing wrong with saying, “I have no problem doing your taxes for the friends and family rate, not what my boss would charge you”. They can either take that as a polite no or understand that you have to charge them.
Part of learning a trade is learning the business end of the trade. If you are in the business of doing favors you won’t be in the business of making money.