Here is a quote from the whitehouse website:
Quantity and frequency of sales are relevant indicators. There is no specific threshold number of firearms purchased or sold that triggers the licensure requirement. But it is important to note that even a few transactions, when combined with other evidence, can be sufficient to establish that a person is “engaged in the business.” For example, courts have upheld convictions for dealing without a license when as few as two firearms were sold or when only one or two transactions took place, when other factors also were present.
With potentially more ATF agents and correlated funding on the way, are we in trouble?