One factor that influences your credibility is the quality and relevance of your supporting materials.

This is a true statement. Quality and relevance are huge factors in the credibility of an argument, and by extension, the person making the argument. Poorly sourced or poorly referenced articles and arguments can make the reader tune-out very quickly and make the author's points almost useless. Irrelevant sources can lead the reader to faulty conclusions and premises that simply do not fit the argument.

The answer would definitely false