That your Meetup was free doesn’t mean that you will also be holding private meeting with people for free. You should let them know that only your pre-planned meetings or seminar will be free and when that day comes you can teach them a lot of things they would like to know for free, but apart from that date you shouldn’t be seeing anyone and answering questions for free.
Anyone that has a question to should pay before you meet them privately and answer questions. And of course some of them might stop calling you because they only prefer free things lol, only those that are serious enough to learn about Bitcoin will keep calling you.
This is definitely an option, and it is very common in many other industries and this could solve the problems of the OP, as soon as anyone wants to get a private consultation from him the first thing that should come out of his mouth is the price of the consultation and if the customer does not want to pay then kindly suggest them some free sources from which he can keep learning and then cut him off, this has many advantages, it will save time, you are still being helpful and it may bring a customer in the future and if done enough times it will bring you money.