Hah - I'm like you, I tend to only believe in things I can, or have seen.
I have read a few fibs on these forums, but they usually aren't about total yield, they're usually about how long it took to grow the plant. For some odd reason, beginner growers don't want to admit how long it took the plant to grow. I've seen pictures of well-established vegetative plants, with a dozen nodes, under 100 watts of lighting, and a caption saying 'Day 14 from seed' or something to that effect. Nope, more like day 40 from seed. There's no shame is vegging a plant for 50+ days, it isn't a race, and you don't win anything for finishing first, or taking less time than the next guy.
It's a lot more helpful to other forum users if we post truths. That way everyone knows where they stand, and knows what's involved in growing (techniques, time-scales and end product).
Peace