Step 1. Step outside your home and close the door.
Step 2. Ask for the officers’ ID. Write down their names and numbers.
Step 3. Ask if they have a warrant. If they can’t produce one, tell them that if they don’t leave, they’re trespassing and you’ll call the Sheriff.
Step 4. NOW if they don’t leave, I’d think you have legal cause against them, even personally.
If you do that, they will serve you and you have to go a hearing and explain why you didn’t show them or they will get a warrant, if they can. Seems to me the burden of proof it on them. If one wants to purchase 50 guns in a week, it’s none of their business as long as they were purchased legally. If they have reason to believe you are selling guns to Mexico or whomever, they should have to have some proof other than the fact that you purchased guns which you constitutionally have the right to do. FTATF!