Everyone has a price.
But prolonged exposition and mutual relationships (even ones kickstarted by selfish, careless objectives such as "Pay me!" or "Go to war for me!") necessarily lead to intertwining of identities. And once you consider something (or someone) a part / extension of yourself, caring follows.
In other words, given enough time and substantial interaction, the lines between "you" and "me" blur. That's just a biological (physical?) observation; cf. parasites and symbionts, nation building, product marketing, leadership…
Of course it's a scale, not a binary care / don't care. A doctor may care very little about a celebrity he knows he'll be interacting with for a year or two, max. But family doctors still exist, too.
IMO it's down to arguing semantics about how "tight" is the causal chain between the cause and effect.
Do you perceive the cause (repeat buying) and its inevitable effect (caring) as sufficiently distinct in time and space? Then I guess you didn't buy the caring, you "built it through repeated interactions".
I personally see that boundary as mostly linguistic, and tend to not draw the distinction.