Given that software as a arena is a widely competitive and rapidly evolving one, you can never know if the person in front of you is an expert or not. In such a case, what has always helped me is to first remind myself to be humble and use this cheatsheet:

* ask questions that probe your point of concern, instead of pointing out flaws. This allows the other person to reveal his expertise with a solution and also enlighten you in the process or admit their mistake.

* Never claim to know everything. Always be cognizant of the fact that other people ("newer" people) will show you up. Always be willing to learn from anybody who makes a concise argument.