There are subjects in which I have formal training and extensive experience in. Here I speak with authority and don't use slippery language; I may even cite sources.
There are other subjects that I read about once probably somewhere on the internet at some point in the last 25 years or so. Here I will phrase it as "If I understand correctly" or I might even pose it as a question inviting others to correct me.
I went to flight school during the time when we all thought System of a Down had recorded a song about the Legend of Zelda. If you don't have an internal rating system about how reliably you "know" the things you "know" you're probably not worth listening to.
My college public speaking teacher was also so sure that "wuddn't" is not a word. y'all gotta problem w'how I tawk can get axe fucked. I'm drunk enough to let out the drawl, c'mon nao.
I will use slippery language for every statement unless you are family or you are paying 100$/hr 4 hours minimum.
And then I will phrase in terms of "the trade offs and decisions that are available to you and why"
That may or may not be the case, it's true that you get what you pay for but sometimes you also get more than you bargained for. Really, it's up to you and your risk tolerance level about possibly over paying for advice or risk missing out on a valuable advice. Anyway, I'm not here to tell you what to do, because you're paying me enough.
I think a problem might be that even if you have an internal rating system, it's still a spectrum and the other person doesn't know what that percentage of confidence you have is. If you're 95℅ sure, maybe you still want to communicate that it isn't 100℅ since assuming you're 100℅ sure might cause problems.
Things change all the time, even if it's part of your field of expertise. Today, gorillas are technically monkeys and Pluto isn't a planet, but lots of people are sure those aren't true.
Lotta potential positions you could take with regards to that system, y'know. cracks epistemological knuckles, what ya got? How do you decide how much weight to attribute to a fact you heard someone else tell you? Who? In what context? That stuff doesn't, I believe, have a pithy answer