On reason... On faith...
So, which advice would you give?
In the real world, it depends. With most people in practice, assuming they have enough of an understanding of me to know I am a skeptic on these things and are implicitly asking for one or the other, I give that. Therefore I normally give advice on faith.
I've raised arguments for philosophical scepticism before, which have mostly been argued against in a Popper-esque manner of arguing that even if we don't know anything with certainty, we can have legitimate knowledge on probabilities.
The problem with this, however, is how you answer a sceptic about the notion of probability having a correlation with reality. Probability depends upon axioms of probability- how are said axioms to be justified? It can't be by definition, or it has no correlation to reality.