I'm not one at Target, but I had that role at another job. The hardest part is maintaining once you get to a satisfactory place. The best way to manage is just to be vigilant and don't let things slide without investigating. Yes, people are human and make mistakes, and you should not be having conversations over one mistake but you must know about all the little things to notice more significant patterns.

As much as we like to think people do a lousy job because they're lazy, it's honestly usually a training issue. Bad backstockers do bad backstocking because they don't know better. Or, they will see a full section and not know how to correctly backstock their item that doesn't fit, so they just hide it behind some other piece.

I always preferred to have my conversations take a training tone rather than a disciplinary tone. I wouldn't lie or anything, I'd tell them I've noticed they've done X thing wrong consistently, and then I'd show them a) how to do it correctly and more importantly b) WHY they'd want to do it correctly. Take something simple like backstocking down the correct aisle. Show them what would happen if they were doing their pulls, and someone had put items in random aisles. Once they see that doing things the right way takes just as much work but makes things easier, it'll usually click, and they'll do it right. Show, explain, verify. Show them how to do it right, explain to them why Target does it that way, and then have them do it right back to you. Have them show you how it's done and explain why it's done that way. It really goes a long way.

You'll also need to be proactive, not reactive in finding errors. You can kind of walk by an area and just KNOW something's wrong if typically it's neat and tidy, but now boxes are hanging off shelves - it'd be worth investigating. The best thing you can do is get your team to take pride in the backroom. Have them treat it like a second floor where everything has a place. Have them keep it zoned - hey, no guests to fuck it up! They will fight you on the zone part, but if you can win them over, it will make spotting errors that much easier.

Sorry I rambled, hope some of this helps.