My question involves criminal law for the state of: CA

I have a friend that is freaking out because he believes an old client of his may report him for trafficking drugs through the mail. This process seems quite anonymous and I'm curious how far an anonymous tip can be used to indict someone. This person has plenty of information about the operation but the quantities wern't large enough for a federal case to really take off on. Perhaps 1/4lb of weed every now and then and maybe some e. Since then my friend has relocated to another state so it would be hard to find/investigate it at all. Any information would be helpful