Am I financialy enabling child labor in 3rd world country by buying second hand fast fashion from Thrift shop and Vinted? Because I am not the one who originally bought the clothes from Shein. But buy buying it again from someone else I still use it uhhuhh this is complicated.
Unlike an expensive phone, where the initial purchase may have been made with the expectation to still get a couple hundred after a few years, I see no connection whatsoever between your buying second hand fast fashion and the first buyer’s purchase decision. They would have bought it regardless of whether it would become trash or second hand.
In short: no.