Answer:
Reliable.
Step-by-step explanation:
A scientific theory is the best model we have so far to describe a phenomena. I say "best model" because no scientific theory is the absolute truth; data from new experiments has potential to modify or even replace a theory with a new one, which can now explain the new data along with the previous observations.
You can come to trust new theories as they pass more and more tests, but you must always remember to have some skepticism because you never know whether your theory will agree with the new data from your next experiment.