You (can) bet your boots spoken language
You can firmly believe that something will take place. Sometimes said ironically.
You can bet your boots that the bank robber will be caught soon.
They had paid you money, so you can bet your boots that they will come back to take what they bought.
With such an immaculate performance, you can bet your boots she will be the winner.
Meaning absolutely certain or without a doubt
That's absolutely right.
Totally certain.
With absolute certainty; decisively
You can be absolutely certain that something is true or will occur.
The origin of this phrase is not clear.