Correct forms of address

Hi Stephen,

the concept of having two ways of addressing someone can take sometime to get used to, especially if you native language doesn't differentiate between the two.

Using "Sie" and "du" to address someone hasn't lost it's importance and is still the foundation of daily interaction.

As a rule of thumb you can say that you use "Sie" for everyone that hasn't offered you to use "du". Basically, if you know a person well and are friendly with them you use "du". For everyone else use "Sie". For example say "du" to your extended family and friends, but use "Sie" for all strangers and superiors, like older people and your boss.

Some people might think it's rude if you don't address them correctly, however if they realize that you have just started to learn German they should be very forgiving and help you out.

If in doubt always use "Sie".
It's less offending to say "Sie" to someone you know, than "du" to someone you don't know.

In your case you should have said: Woher kommen Sie?
Unless the lady ran out of the book store screaming, I'm sure she wasn't too worried.