I've been to a number of fundraisers that had both baskets, where you buy tickets, and put as many tickets in as many baskets as you want, and spend as much as you choose, and the winning ticket wins the item. There are also 50/50 drawings, and a number of other drawings. The ones my group of friends and I usually attend are fundraisers for private schools, churches, or other organizations. We've never given back anything we've won.
And as far as I can tell, no one has ever refused a basket or prize they won either, in my group, or overall, because they had "already won" one or more. In fact, the last one I went to had both an Android tablet, and Ipad as two of the grand prizes, and someone in my group, won both! and kept both! Now some people may say she should have chosen one, and refused the other, being that they were essentially the same thing, but I disagree. She bought tickets for each, and just happened to get lucky and win both. She had the same chance everyone else did, and just got very very lucky.
And I've seen some people win 6, 7 10 prizes. its the luck of the draw, and if they choose to spend several hundred dollars on chances to win vs. my $50 or so, fabulous. Then its likely they will win more!
the one and only time I saw anyone give back their 50/50 winnings, was when it was for a local catholic HS, and i believe one of the parent's won, and donated it back. But in all that I've attended, its never been suggested that the winner give it back, and that's the only time I've seen it done.