In her case, she put too much force into it and fell on her ass. She won and when the show came back from break to do the Showcase, she was on crutches. I imagine CBS's lawyers were waiting for her at the hospital. The thing that gets me though is that people try to spin the wheel harder than they need to and that's why it stopping on a dollar doesn't happen very often. I just saw a dude spin the wheel so hard, the numbers actually blurred a little.
If it was me, I'd would just put enough force into the spin to get it around once and get it to land as close to the dollar mark as possible. I'm not saying it even would, but the success rate would probably be higher.