Ask for a lawyer.
You have the right to be advised by counsel and should immediately ask to have your attorney present if an investigator comes to your property.
If in doubt, don’t’ talk.
The Constitution gives you the right to remain silent. If you have any doubt about whether you should answer questions from law enforcement, politely decline to answer and direct investigators to contact your attorney.
If in doubt, ask to see a warrant.
Law enforcement generally must have a warrant to enter buildings or inspect documents on your property. If you are unsure if an investigator has the right to enter your property, ask to see the search warrant. If they don’t have one, politely decline to let them enter and contact your attorney.
Get it on tape.
Sadly, not all law enforcement officials tell the truth. Smart phones make recording cheap and easy. After informing law enforcement you will be taping, record your interaction and save the recording so there’s definitive proof of the events of their visit.