Cash. You finish up from donating, you walk to the back, and there's a little checkout area. Everything's automated and they know how much you're due to receive. They hand you cold hard cash.

Also, (this one is big with me)the entire place is insanely clean. It's not some gross place with people looking for a quick buck. It's a very legitimate place and everything is very clean/sanitary. The needles they stick you with are one time/disposable and you watch them unseal them right in front of you.