Swamped

You look around quickly for a back entrance. If the thief is startled, they'll try to leave that way, probably in a hurry.

And there is one. There's also a trash box nearby, which looks to have mostly scrap iron in it. You move it in front of the doorway - the door opens outward, so it'll run into the box. And you can say with confidence it's heavy enough that just swinging a door won't move it out of place.

Now that you've set your little trap, it's time to spring it. As safely as possible. You knock on the door.

The light suddenly fades out. And you don't hear anything - especially not a door running into a trash box.

So you think they've opted to hide rather than running. An odd choice, but you suppose it makes some sense - if you come inside, they might be able to ambush you. Still, you're hardly without protection, so it seems worth the risk.

You pull the door open and look inside. No ambush yet - they probably haven't spotted you yet, since you haven't actually entered. Or they're just trying to stay hidden.

Either way, it gives you a glimpse at what's in there. Maybe you can spot something helpful.