It's not about one factory farmer being connected so directly to your specific choices, it's more like: restauranteers and grocers increasingly notice customers insisting on local, humanely raised, grass-fed beef, and thus they reduce their factory-meat order size and quantity. Factory farmer asks why, maybe gets an answer and thinks about improving conditions, or maybe doesn't in which case it's still a net win as the market share shifts in favor of the "good guys".
A) I buy my meat at the farmer's market.
B) I buy tempeh instead of meat.