Claims must always be supported by evidence such as
Facts, statistics, quotations, examples, hypotheticals.
In any work where one has to produce or make a claim, it is important to support one's claim with sufficient facts, statistics and quotations, examples and even hypothetical assumptions. If these factors are met, then it will be easier for the readers to understand and know the claims made by the writer as true.
For any form of argument, the proof of the claim is important. If these factors are available for the readers or the one judging the work, then it will also be easier to understand and even maybe accept the authenticity of the given work.