How do you counter the assertion: "Asymmetrical trade deals and resource extraction are justified because client states approve of it" ?

all bourgeois transactions are coerced. you should counter this the same way that you counter reactionaries who claim that the relationship between owner and worker is "consensual" because the worker "freely" fills out an application and "asks" the business owner for a job, as though the job itself were an object of desire, rather than something the worker seeks out because the alternative (homelessness, poverty, starvation, death) is even worse. No worker wants to be exploited by a capitalist for surplus value.

As for client states and imperial core states... well it's similar, just on a bigger level. But you also have the element of the "comprador bourgeoisie" (who fuck over their own nations' development to feed superprofits to the imperial core capitalist) who are distinct from the "national bourgeoisie" (who exploit the proletariat but still perform the true historical role of the bourgeoisie which is to break up pre-capitalist economic formations and develop productive forces.)