I've been around relic hunters for many years, most of them understand that Uncle Sam tends to frown upon folks walking around with metal detectors in our national parks. But occasionally you have some greedy dork who missed class that day.
On a related note, I was watching Junkin the other night (which is a sort of redneck Antiques Roadshow) and they came accross some guy at an Alabama flea market with a "CS" buckle with a minie ball stuck halfway through it. Wanted $100 for it. That sounds more than a little fishy to me. I'd bet my last paycheck that it's a fake. I have no idea what buckles are bringing at the shows, but I think it's a safe bet that they bring more than a hundred bucks, 'specially one with a bullet sticking through it.