> If you get flagged, you need to prove you made less than $600 in profits which is difficult.

That's not true. The $600 boundary is meaningless when it comes to computing the taxes you owe. All you do is write the cost basis of the items you sold. This is easily done. If you donate clothes to goodwill or whatever you already do something similar to this when computing the value of your charitable deduction.

> My total sales amount to $3000+. This will definitely raise a red flag but nothing I sold was for profit

Why would it raise a red flag? You just fill out the basis on a 1099.