Please, if people click on my brand let them see only my collection, even if someone else try to copy my brand. Show bad sellers crappy "designs" only when people find and click their listing or their copied brand name. You can add a Designer name next to Brand Name to not confuse customers.
You could show:
Brand AAA of sellers xxx
Brand AAA of seller yyy
When customer type a brand in the bar you could show first seller with older uploading data/Best quality design/best returning percentage/best customer review