Cheated by gardeners - anything else Auntie could've done differently?

Recently my aunt hired independent gardeners to make over the entire backyard of her house. Obviously nothing had to be written down or signed, Auntie paid in cash. Being the type that knew every cent in her wallet and possessing impossibly sticky fingers, she got into an argument with gardeners when they returned the next day, claiming she’d missed one $100 bill. In the end, feeling betrayed and cheated but unable to negotiate well, she yielded.

She said she double-counted, triple-counted, etc., the wad before handing it over to the men. I asked her if she counted the bills IN FRONT OF them, like cashiers would; no, she didn’t.

My question: Was there anything Auntie could have done differently? Would counting the bills in front of the men prevent this kind of occurrence? Do you have similar stories to share? Much thanks for any input.