Very, very few small FFL dealers make a profit.
The language is predominantly to earn a profit the amount is not specified. If the activity was done with the express purpose of earning a profit the amount of that profit is irrelevant legally. The criteria is simple did you buy and sell guns to make a profit if yes you need a ffl if you are selling surplus guns which there really is no such thing then no. This is first year law school easy. Without even getting into substantial intent. Buying at wholesale and selling at gun shows or back alleys is going to get the jump out boys attention. Selling estate firearms once in a lifetime not so much.