you'll need to PRACTICE the non direct methods. If others heard you say "I don't believe you", then you probably said that or words similar.

"I don't believe you" is confrontational.
"I must be doing something wrong, can you show me what to do." says the same thing, "it ain't working", but then you've asked for help. Even when you know you've done everything right.

But it does take practice. And a conscious effort ask in the "non agressive" (mealy mouth) way.

And it does work very effectively.