Re: Where did you get that $20 padlock?
"Put a little tension on the hasp and tap either side of the body"
A problem with most 'snap-shut' type padlocks. The bolt is spring-loaded so as to allow the shackle to depress it when closing. Anything that can jostle the bolt back and forth (smacking it or a thin metal shim) can get it back open.
Better padlocks have the equivalent of deadbolts and key retention. You need the key to positively rotate the bolt into the locked position. And you can't take the key out unless the shackle is closed.