Are the apps which check if a phone is rooted reliable?

[AC Question]

Recently, i had an issue with my lcd lg screen on Lg g3 D855. I went to the lg service, considering that my warranty was ok. But the answer of the service was that my know has been rooted by an app, so there wasn't any warranty. But i downloaded an app which check my phone if is it rooted, saying that is not! How can i found what the truth is ?

 

[AlphaTango414]

Pulled from XDA.

roma1927
Go to dialer and digit 3845#*855#, tap to "LG RCT", tap "display Result...this is root counter

 

[GiAnast]

Thank you! You are blessed! You are saving me! And from this option i see if my phone is rooted right? The Display result says official, so it hasn't been rooted. Right? Because the last time lg services said to me that was rooted!