Good website copywriting is honest, even when it means comparing yourself to the rest. If you’re going to compare your company, product or service to the competition, you need to be honest. Naturally you want to mention the differences that put you ahead of the competition, but don’t short change the competition or make up negatives they really don’t have—that tells the reader they can’t trust what you have to say.
Source: expresswriters.com, 11 Website Copywriting Secrets (That We Will Tell), #10
What does "short change" mean in the context above?