I've seen people routinely abuse sick days and they considered it normal (they brag about it). Others coincidentally are "sick" for exactly 10 days a year, year after year. They think management doesn't notice, and wonder why they don't get much in the way of raises or promotions.

Basically, you're right. The verification thing is invoked to provide convenient evidence to get rid of someone they already want to get rid of.

Trust only goes so far. If a company does not have good cost control and verification procedures, they can and will get robbed blind. Heck, the cash register was invented by a bar owner who suspected the bartender was embezzling in a blatant and ruinous fashion.