Here is a good excerpt from OwnTheDollar.com that gives their insight on when the IRS is involved with precious metals.
"What Levels Trigger IRS Reporting?
The Internal Revenue Service’s reporting requirements for precious metals dealers varies based on the type of gold or silver that is being traded. In most cases, reportable sales of gold are triggered when twenty-five or more ounces are traded in a single transaction. Incidentally, there is actually not IRS gold reporting requirements for American Gold Eagles regardless of the quantity traded. Only pre-1965 U.S. silver coins sales are reportable when the sale’s face value totals more than $10,000. Like most financial transactions, $10,000 is usually the magic number that draws IRS scrutiny. And IRS gold reporting is no different."
In short, if you engage is transactions less than $10,000 generally there is no IRS involvement at all.