Difference between being the Brand and selling other brands?

Dear fellow Amazon sellers,

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I have a very important question, i’m the owner of the Amazon Marketplaces of the company i’m working but we are our own brand. Now i probably have a new job but they are a re-seller of multiple brands. What are the big differences i need to pay attention too? I know i can’t change the content wise and such am i right if i’m using the same EAN as them? Got any more quick tips?