Every growing online seller in Thailand eventually faces the same build-or-buy decision about marketing. Building in-house means salaries, management overhead, and a hiring market where good e-commerce marketers are scarce and expensive. Buying means choosing between two models that look similar on a proposal but behave very differently over twelve months: the traditional agency and the partner model. The difference isn’t branding. It’s structured how the work is scoped, how the incentives point, and who carries the thinking. Choosing wrong doesn’t just waste a retainer; it costs a year of compounding you don’t get back.