Being Polite
I always thought you were suppose to use usted or té when you were talking to someone older than you, or someone you don't know that well to be polite, but I've had a few people tell me to not use that because it makes them feel old. I get confused because when am I suppose to use it? I think I might just use it if I'm ever in Mexico and get arrested, and have to talk to the cops : ) I'm kidding!
3 Answers
If you want to be safe, always use the formal tense until they say otherwise. That's the most formal and safest way to go.
If someone asks you not to do it, it would be impolite to continue. There are a lot of Americans that don't want to be called "Ma'am", or "Sir" for the same reason. It's still polite to do so until they say otherwise.
In English there is no difference between usted and tú. How to use them in Spanish is very contextual, depending on the country and the situation. For people you dont know in a more or less formal situation usted is safer.