I would not offer services for free. It is extremely unfair towards everybody who needs to earn a living by doing what you do and it also shows (in my opinion) that you do not honor your own value. I think you should charge what is normally charged and trust that you will build a reputation, but then you won't have to increase pricing down the road, which, as I heard, is the most difficult thing.
Peope want everything for free, but that doesn't mean that they also value it, if they get it for free. If they are looking for help and you can provide it effectively and professionally, how could you justify giving them your service for free. Isn't it worth that they also put in their energy (=money)?
Most people, if they look for professional advice, will not take you seriously if they don't have to pay for you. They will not do what you tell them, since it has this non-commital touch to it, they don't expect much and they do nothing for it. If they pay their hard-earned money, they have a clear-cut expectancy and you have to deliver, and that's a clear deal between you. And they also have to be committed to their own goals, they don't want to throw the money out of the window, so they have to prove to themselves that they did the right thing, that's a huge motivator.