I've been DM'ing randos on LinkedIn for lightweight consults and found that offering to pay up front and asking strangers to price their own time can help to show seriousness and often results in free interactions or buy-me-a-coffee pricing. e.g. "Hey I love your work on X, I've been thinking about / working on related thing Y and would love your feedback on aspect Z. How much $$ to rent your brain for 20 minutes? I'm mainly wondering what you think/know about specific questions A, B, and C." They can either reply with a price, suggest a time for a short call, or just answer directly

Maybe that's linkedin people. There are others like me: there is no such thing as 20 minutes. If I take on something, it's at least 10 hours effective. So we would just flat out refuse any such offer while on the other hand you can get those hours free if the question is sufficiently interesting.