https://www.popehat.com/tag/shut-up/
His writing makes for accessible, knowledgeable and amusing posts on a very serious topic and are extremely well worth a read. But the summary version is pretty straight forward: there is no such thing as an out-of-the-blue innocent visit from Law Enforcement, ever. This is kind of common sense when you stop think about it: agents are not free and budget is not infinite. If they are actually devoting an actual warm body to talk to you, particularly a warm body to visit you, it is always, always potentially serious. It is not on a lark, they did not roll some dice and have your number come up for a community chat. They're talking to you for a reason and given their fundamental purpose that reason may be quite bad for you, whether you did anything wrong or not. The true super power of government is patience and grinding, relentless inertia. By the time they talk to you odds are high that they have already done their research, extensively. They have a legal theory and narrative already in mind. If the Feds are knocking it's time to get a lawyer, period, particularly if you're fully innocent.