It would be pretty terrible if we found out the detections were mistaken or even fraudulent.
From what I can understand, LIGO's results seem very open to interpretation. It seems like they could be mistaking noise for signal. And it even seems possible that some unscrupulous person(s) could have created fake signals, using something like the "blind injection" mechanism.
Extraordinary claims require extraordinary evidence. It doesn't seem like the evidence is strong enough yet to say definitively that GW even exist.