I don't brush my teeth because other people word.
I'm doing it for the feeling of freshness and believe it's good for me because of what I believe to know from science and personal expeirience about existence and influence of microorganisms.
I try to avoid putting qtips in my ears even though people are doing it because science says that it has higher probability of doing harm than good.
> Other people can also say the craziest things and pass it off as science.
That doesn't make it science and you should base your decisions on science not things passed as science. You should use your critical faculties and knowledge of scientific process to tell what science is and what is not.
You definitely should verify every single thing that informs your decision proces if the decision you are about to make is an important one.
> ... Sometimes those heuristics lead people to do something different that ends up being the better way to do things than what science at the time entails.
Science offers heuristics to guide your decision process. If scientific heuristic exists and you are using your own instead, you are doing wrong (even if by chance it ends up well).
If there's no scientific heuristic for given problem ( you need to check! ) then by all means make up your own. You won't be wrong unless you make "let's ignore what science established" a part of your heuristic.
You'd be amazed how much of the things you consider instincts filling gaps in science was actually researched for very practical fields. A lot. When money is on the line people suddenly get very interested in actual reality and they do the research. Some of those instincts get confirmed, some get thoroughly debunked. There was no knowledge untill science properly investigated it. Just self propagating ideas, right or wrong.