The usage of "WHO" as a conjunction [closed]

As BillJ said, indifferent to the ways of mercantilism and minimum-wage expectations is an adjective phrase functioning as a post-head modifier. The way it is written, it is somewhat ambiguous whether it modifies the subject (I, the speaker/writer) or the cashier (in which case the adjective phrase is an internal modifier of the noun phrase that is the complement of the preposition to). Grammatically, it could be either, though I should add that the absence of a comma before indifferent makes me think it is more likely that the writer meant it to refer to cashier. Unfortunately, in this case, even the context doesn't completely remove the ambiguity.

Just to make sure that the adjective phrase could indeed modify either word, note that both of these are acceptable:

Thus British tyranny mercilessly increases the sufferings of the world, indifferent to the laws of humanity. (source; here it modifies the subject, British tyranny)

Dunn likens those who produce and market alcoholic beverages to the robbers who stripped and beat the traveller on the road from Jerusalem to Jericho (Luke 10:30-37), the drunkard to the victim of their crime, and those who passed the beaten man to a public indifferent to the availability of alcoholic beverages. (source; here the adjective phrase is an internal modifier of an NP that is the complement of a preposition)