This is really, really bad behavior. The Washington Post has traced down an image of Trump posing with a $12,000 helmet that he purchased with money explicitly raised for charity:
Four years ago, at a charity fundraiser in Palm Beach, Donald Trump got into a bidding war at the evening’s live auction. The items up for sale: A Denver Broncos helmet, autographed by then-star quarterback Tim Tebow, and a Tebow jersey. Trump won, eventually, with a bid of $12,000. Afterward, he posed with the helmet.[…] But Trump didn’t actually pay with his own money. Instead, the Susan G. Komen organization — the breast-cancer nonprofit that hosted the party — got a $12,000 payment from another nonprofit, the Donald J. Trump Foundation.