If you're in court--that is, you were sued or sued them--then what they say matters: it  is testimony and evidence that the court will consider in deciding who was at fault, who must pay how much to whom, etc. You should counter with your own evidence and testimony, including the testimony of other witnesses who will support or bolster what you say. The court will weigh all the evidence, all the testimony, and the apparent credibility of the witnesses in coming to a judgment.