Always and never.
As long as the sensory circuitry is in place (nerves and such), you can only trust that the information is transmitted correctly. This probably doesn't make too much sense, but when you dream, you see smell and feel etc, but all of that is created in your brain. So is it true? Depends on how you wish to define truth. If you mean actuality, reality, then what you're dreaming is not actually happening, but your brain thinks it is... in a way.
So as far as sense transmit information, all you can hope to trust is that they are transmitting correctly. (that's the always part)
That's a more rational/scientific way of looking at it.
Honestly, when I first saw this, I was thinking along a different line, like when can I trust my general 'sense' of a person to match 'reality'. Meaning if I meet someone, and I think I get a sense of them, then how close is that to reality...and that really depends on the skill/acuity level of the person.
As an aside, in an INFJ forum, I think you'll get all possible sides of the answer, but maybe no definite answer
I'm interested in seeing how this goes.
I'm a little crazy right now, so if that didn't make sense, I'll be back in about 5 hours to clear it all up...