Not all ideas are great ideas. As a Product Manager, I understand that saying no in the right way for the right reasons will help you gain respect and authority in your organization.
Whenever there is an idea being discussed where I feel the direction is not right, I don’t say no immediately. I listen to it carefully make sure that the other person feels heard. Now based on the audience, I tackle the situation differently.
In case the audience has important people north of you like the CEO or Board of Directors, I would mostly reply that I need to think about the suggestion, discuss it with my team and then get back by a specific date. It’s very important to not get be intimidated and get pushed around. When that day comes, I will be well prepared to explain why the idea doesn’t make sense at this time.
Sometimes I say no right away. If I have a clear product strategy and goals unsuitable ideas are easy to evaluate. E.g. In my firm, business floated an idea of sending a static OTP to the customer all the time. This would make it easy for the person on-boarding the customer to fill that static value all the time instead of asking the customer. Now, for this it was easy to explain how this idea breached the regulations and security and how its very bad to implement. Of course, you still want to make the person feel heard before you explain why we aren’t going to do that right now.