Golden is their hair, and golden is the wealth they mine from the Westerlands. The power and influence of the Lannisters cannot be overstated.
It is as much a threat as a promise for Lannisters to say that they always pay their debts. Fealty provides great returns, and loyalty is richly rewarded. Rebellion and insubordination is destroyed root and stem, as the Reynes of Castamere could attest if any were left alive. No one doubts Lannister subtlety, for this is the family whose ancestor Lann the Clever used only his wits to gain the stronghold of Casterly Rock and stole gold from the sun to adorn his hair.
Loyal Lannister vassals know how to wield their gold to good effect. They cannot, perhaps, ever be quite as rich as a Lannister, but their liege lords do not begrudge the effort. Deep pockets full of gold, and the backing of a lion of the west, goes a long way to security among the merchants of the world—and in the shifting allegiances at court. Should you visit the dockside bazaar of Lannisport, you can haggle and trade, but you may end up with more than you bargained for—because nothing is without cost.
You are unparalleled in running the engines of an economy, which serves you well in the purchase and sale of power. Your opponents will quake when you show them your teeth, when you shout Hear Me Roar.