"How hard is it to know who you are employing? If your staff retention is really so poor that this is impossible then you have a larger problem than not being able to identify people."

And that problem has two horns (just like any well-bred dilemma): bad pay and bad working conditions. You show me an organization with high staff turnover and I'll show you an orgnanization with (a) sub-human pay levels (b) very probably excessive management pay levels and (c) working conditions and management attitudes that far transcend the worst that Dickens wrote about.

It's not easy motivating people in such jobs, but it's not impossible if you remember that they are humans too, not just meat-robots.