Am I obligated to ascertain the truth of rumours that the eruv in my town is not being maintained properly; this was supposedly said by an eruv expert who was involved in the eruv’s construction several years ago, if a) it is hard for me to get to speak to this expert, b) the certifying authority, generally regarded as reliable, still stands behind it and c) I know that there are fellow residents who are opposed to the eruv in principle? While many of these people are entirely noble, others have sought to use rather devious means to fight against the eruv in the past.
If you rely on the certifying authority then you can rely on his eruv. However, it may be prudent to find out what is being said and bring it up with this authority. Perhaps there are things that have been overlooked. While many eruv disputes go over board, honest debate and constructive criticism is often to the benefit of a community eruv.