I am very far from an expert on any specific culture that is subject to cultural appropriation so I’m not the right person to direct you to ‘legit’ market stands.
But, ya know, here’s my common sense kinda thoughts:
If you want to know whether a person selling stuff from a specific culture is (a) actually from that culture and (b) has given considerable thought to the topic of cultural appropriation and © has produced things that they feel are respectful to buy if you’re white, the most obvious questionto ask yourself is probably ‘are they writing about these things in a segment on their flyer/webshop/blog etc?’. If a webshop has a segment where they acknowledge that cultural appropriation is a real thing and explain how their products try to avoid it, that seems pretty ‘legit’. You can also check what other people from that culture have written about that store.
Use your brain. Read about the stuff you want. Use common sense.
But just as important: accept that people within a colonized culture are going to have different opinions on what is respectful.
Accept that people within colonized cultures can disagree on something and you can never be a perfect ally to all of them. But don’t just choose and puck whatever opinion is most convenient to you. Actually listen and think. The first 9 people you meet might see your new t-shirt and think it is a respectful purchase from a great designer from their culture, but the 10th person might still be upset that you are taking another thing that is great about their culture and wearing it as your own, looking cool through the coolness of the colonized other. Especially if you’re clearly showing off how stylish you are through your clothing from other cultures. Don’t dismiss them. Accept that that 10th person might still have a very valid point. Listen to their arguments and use your brain again. Be prepared to be wrong and to admit it.
