“Let me get back to you on that.” This phrase may seem harmless, but it sounds like a dodge. Know your capabilities and speak with confidence. If you’re asked something you don’t know, say so outright: “I’m not sure, but I’ll find out.”
“In my opinion…” This commonly used phrase undermines your point of view. Even if you don’t intend to, it carries a suggestion of bias. Instead, say “I think…” or “My experience suggests….”
“I could be wrong.” You may be shooting for humility with this phrase, but it comes off as uncertain and unconvincing. If you state a fact, do so with confidence. If there’s a significant chance you’re wrong, lead off with something like “It’s possible…” or don’t say it at all.