that's stupid, though. your character would not go out of their way to call someone 'ser' simply because it's a class issue - by falsely attributing rank, you are disrespecting the class you are referencing and potentially the person you are speaking to. unlike lord/ladyship, which sycophancy allows characters to call when referring to anyone above their own station, 'ser' is exclusive to a very well-defined (and limited) group of people. unless people are outright introduced as knights, your character wouldn't assume that to be their position.

there are very many ways to (im)politely address people in Westeros, depending on your character's breeding/speech patters. defaulting to 'ser' just makes it seem as if you're not willing to do a bit of thinking on the issue.