I don't put the money down - the stack of bills stays in my hands. the unchecked ones go between index and middle finger, checked ones go between middle finger and ring finger - it's awkward at first but now it is the only process I use and it's fast.
I have also turned away obviously fake bills. If you handle money for a long time, you can pretty much feel the difference. If the bill fails in the machine, I hold it up to the light to see if I see the written strip inside. If they are older and don't have the strip I will use the pen.
Had a man not to long ago try to give me obviously fake 10's, a whole stack of them . I looked at them and asked for a different form of payment. I said - you should go back to whoever gave you these, because they are not real. They were all photocopies and all had the same serial numbers..They weren't' even cut evenly.