It depends where those leads are coming from. If your close friends are the ones asking you for advice, then they are probably aware of how valuable you are as a friend, and (hopefully) try and pay that back, or forward, in their own way. I would not advise charging these individuals for your wisdom - it may cheapen your relationship.
If they are not your close friends, asking for financial compensation for your ear and time, in my opinion, is more than reasonable. Time is money, and a non-renewable asset. If they are unwilling to compensate you in some form - than your wisdom may not be as valuable a product in the market place as you think.
With the above taken into consideration, there may be a third way. My father, CEO of Vollett Executive Coaching has successfully sold his coaching-ability through an "influencer strategy", which involves almost no digital marketing, or marketing spend of any kind, and has resulted in 15 years of steady work.
Feel free to book time with me if you would like to learn more.