Another suggestion is let him be their while helping him buy Bitcoin, so he can learn against next time. I had this guy that was on my neck any time he want to buy any coin, luckily for him he didn't buy Bitcoin but another coin and he profited quickly due to the nature of altcoins and all of a sudden, he start coming with different phone to help him buy coin for some of his colleagues and he didn't know how to do simple but and sell. I thought him this time and I never saw his traces again.
I wouldn't even suggest doing that. When a person approaches you that they want to learn about Bitcoin or cryptocurrencies in general, direct them towards resources that they can read and ask them to do a lot of research so that they get enough knowledge before they get started, this will help them in their journey and they won't bother anyone whenever they need to buy something or make an investment.
It is also essential for an investor to understand everything before they get into the market, they need to know what is a wallet, which wallet is best for short-term or long-term holding of cryptocurrencies, what exchanges they should use, how they can research and find out which cryptocurrencies are trending, etc.
Once they are done with that, they wouldn't face a lot of problems because they would already know what they need to do and where they need to start from.