I think you will be genuinely surprised how little customers care about price relative to other things, even in a market where one suspects that price would be the only differentiator. (I mean, come on, if you're shopping around for an N% discount at Best Buy "clearly" you want the best N, right? Three years ago I thought that teachers were "clearly" universally as stingy as their reputation suggested.)
Trying to differentiate yourself primarily on price will give you ulcers because you'll always be one basis point away from losing to the next guy with more stupid money to burn (e.g. a funded competitor who can afford to have their spread go negative to gain market share, because their objective isn't to run profitably but rather to goose metrics then flip), and you'll attract disproportionately pathological customers who will be loyal to you only as long as no one else offers a better deal. Pathological customers will find every possible way to botch the transaction and blame you for it. (I tried using your Apple B's card to buy an iPod and it didn't work!! YOU THIEF!!!)
Trying to differentiate yourself primarily on price will give you ulcers because you'll always be one basis point away from losing to the next guy with more stupid money to burn (e.g. a funded competitor who can afford to have their spread go negative to gain market share, because their objective isn't to run profitably but rather to goose metrics then flip), and you'll attract disproportionately pathological customers who will be loyal to you only as long as no one else offers a better deal. Pathological customers will find every possible way to botch the transaction and blame you for it. (I tried using your Apple B's card to buy an iPod and it didn't work!! YOU THIEF!!!)