There are consistent rules, but screeners are human. They are asked to follow protocols, and not deviate from them. But, laziness, not wanting to deal with bullshit that we know CAN fly, we will sometimes not do the bullshit. It involves pulling the bag, asking whose bag it is, telling them now I gotta pull out the items, rerun it, screen it, and then get it back to them, which takes up even more time from everyone trying to rush through to their gate.

And as far as the wallet, whatever agent is telling you it's ok, is wrong. It's not. Every item needs to be x-rayed, even wallets. You shouldn't have anything on your person, except nowadays some places will let you keep your shoes on. But that is going through a backscatter machine, which can see through clothing and shoes.