Many believe free will is having the ability to make your own choices without outside influence. But everything you see, hear and smell is an outside influence. Every lesson learnt through past experience is an outside influence. Advertisers have learnt how to subliminally alter our choices without us even being aware of it. How can we ever trust that our decisions have not been influenced?
1) Free will - according to a libertarian view - is defined by the following criteria:
Liberty: Under identical conditions it would be possible to decide or act in a different way than one actually did.
Intelligibility: The actor can explain and show the reasons why he decided and acted as he did.
Authorship: It is the person in question who decides and acts. The person is not forced.
Advocates of free will differ how strict they interpret these criteria. The contra-position to a libertarian view is a deterministic view. Our subjective and conscious experience conforms to a libertarian view. But the only scientific view (neuroscience), which I consider to have the ability to explain the phenomenon, is a deterministic one.
For the whole issue see e.g., Walter, Henrik: Neurophilosophy of Free will. (2001)
2) Of course we are influenced by outside factors. Most of all we are influenced by our previous experiences with our fellow men and with the physical world. In a given situation we do not just react to external stimuli. Instead our reactions depend also on our internal state. The latter is determined by what we have learnt and experienced.
Being totally independent in our decisions would not mean to decide but to play at dice (random choice).