If you don't trust someone because they've lied a lot in the past is it OK to ask them to be literal when they speak?

Well it's surprising that you keep this liar in your life. Asking them to be clear when they speak is OK I guess but youre asking someone to change who they are. Which really is a tough thing for a lot of people. You need to find a way to work on the trust.
Because even the kindest tell little white lies every now and then.

you can try but you will not get it. Liars love to confuse you to pursue their goals