Better the devil you know than the devil you don't. Better be safe than sorry - you are better keeping to what you know than risking something unknown.
Money makes the world go round. Without money, nothing can happen.
For love nor money [I couldn't get him to do it for love nor money]. It didn't matter how much I argued and persuaded, he will not do it. Nothing will make him.
Never look a gift horse in the mouth . Don't look too closely at something that has been given to you - it might not be what you expect. [To find out the age of a horse, you look at its teeth which have particular shapes at different ages.]
Bob doesn't have a leg to stand on. He has nothing to support his argument/statement