Ask HN: Free or not?

Hi HN, Once in a while people from other companies contact me with technical questions like, should I use X in production, how does Y work, what's your experience with Z, can you give info about T, can you share your production experience with A etc.

What do you guys do in such situations? Do you just give as much information as possible and share your experience free OR do you prefer to have a formal relation with those companies and get paid to share your experience (like a consultant)?

Thanks.