The flaw with thay request is that someone could then exploit that system by never using the card once received, selling it for MGP, and then be able to keep on rolling need because they technically don't have the card because they never used it.

Maybe a notification when rolling on the card pointing out you already have it? Something obvious in the pop up description? That would keep the loot rolling fair and make players aware of already having the card if they would rather someone else receive it.