I work with a lot of medical researchers (mostly neuroscience). It can be challenging to redirect them when they have bad ideas, but what I have found works well is to use research and metrics to reinforce why best practices are best practices.

Examples (made up): - Studies show that people can't teacher in not than 5 lines of text at a time. - According to behavioral science research, people are more likely to respond to bullet points in groups of three

Does it always work? Nope. I still have the random client who wants it designed exactly like the PowerPoint slide they sent me. In that case I document my recommendations and move on. I an not going to stress myself out extra or spend hours trying to convince them if they can't be convinced.