The phrase "can bet it" is commonly used in informal conversations to express certainty or confidence about something. As a synonym, you can say "you can count on it," "I guarantee it," "I'm sure of it," "it's a sure thing," or "it's a lock." All these phrases convey the speaker's unwavering belief that what they are saying is true or will happen. Other synonyms include "no doubt," "absolutely," "positively," "certainly," and "definitely." These words and phrases are all useful in expressing confidence while avoiding repetition and keeping conversations engaging.