Go to a member's page and scroll down to the link "Collection". When you open that link, you will see what the member has listed under "Collection", "Wantlist" and "For Sale/Trade". Under the For Sale/Trade, the sports will be listed. Click on the applicable sport for your player and you can then search by name.
The better way is to search your player, go to "Collection Summary" and scroll down to "Reports" where you will find a link "Members with cards from this person on their For Sale/Trade list". That link will list everyone who has any of the player's cards for sale or trade.
If you are looking for a specific card, then go to the card's page and click on "Mentions in Collections". There will be a link at the top of the page to go to the section where it lists who has the card for Trade.
If you are looking for something easier than one of these 3 methods, then you will need to go to another site.
Bruno
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Check my Profile page to see my 2023 Goals and my Lists of sets near completion (5 cards or less) or sets getting close (less than 100 cards missing and 75% complete).
https://www.tcdb.com/Forum.cfm/Page/B/ID/0/?MODE=VIEW&ThreadID=25745&C=0