NASA releases huge amounts of verifiable public-domain data that also matches third-party observations, and its structure is set up to where a hoax is wholly unfeasible.
Are you saying that NASA has never been caught lying, cheating, or manipulating data?
Not as a whole, they haven't. Any organization can have small-scale outlying corruption or mismanagement. I don't think anybody will argue that. But that is also a reason that there cannot be a huge unified top-secret conspiracy. Among the outlying cases, there would be whistle-blowing and blackmailing. Good luck trying to hide the earth's shape from thousands of highly-qualified professionals whose life's work is to know the orbits and functions of satellites. And when a thruster gets stuck open and your satellite gets stuck in the wrong aether current that doesn't match a Kepler orbit, good luck getting help from the contractor responsible without setting off any alarms. Can you imagine how hurt they would be if they found out they had been lied to from the start about something as basic as the shape of the earth? There would definitely be quite a few whistle-blowers. But there aren't any. Not one employee of NASA or any of its many contractors, or any of the other space agencies or their contractors.
So we're left with a choice: Either
A.) NASA has the best indoctrination program in the history of mankind, so that even the disgruntled employees and the people who fail the program still carry the secret to the grave, or
B.) There is no all-encompassing conspiracy, NASA has nothing to hide, and (gasp) you still have more to learn about physics and engineering.