like if he wins 50k, and contacts me, do i ask for his username, and we set up a trade? i'm not too sure how to go about this
Yep, the person who won gives you their username and sets up a trade and then you just bid on the trade with the np (if you are giving pure). If you are giving an item, ask for their username and just send it straight to them, or you could set it up as a trade if you prefer to do it that way. Hope that answers your question.
What NoPoint said + Use a side account or a junk account for the trade. You wouldnt want anyone knowing your Neopets username here.