Well in the Soviet case, plumbing and cheese are most certainly not privately held resources. Doing such work as a plumber means you're essentially acting as self-employed or a business, which is illegal. The cheese is probably produced on a collective farm and sold at a state-owned store.
But surely the cheese case would not be okay even in a Western capitalist context where the store is privately owned. Just replace it with a more scarce product. A store employee isn't allowed to tell customers the store is out of iPhones while keeping a dozen stashed for preferred buyers.
For a Western context, perhaps "tickets to a highly sought after event"
In Western capitalist context, An apple employee can't do that because they would be stealing from Apple. If they are reselling phones that belong to them, they can dispose of them however they like.
I think the Soviet context is key. Because the state is rationing these items, it creates a black market based on personal connections. In Western society nobody cares because (ideally) the market is competitive and you can just buy from someone else.
Yes, an Apple employee doing that would be stealing from Apple. But in the capitalist context, we also have entirely legal business models that I would argue are equivalent to corruption ethically. A business that chooses to sell its products or services only to a select group of customers (entirely legal) and then picks those customers not exclusively based on their finances but based on what else they can provide. Such as access to certain people, different favors, etc. That is IMO ethically questionable.
But the Soviet everyday corruption variety of retail employees reserving cheese for someone who can return favors, that particular thing is particular to a socialist economy with a scarcity of relatively basic goods.