To help explain what I mean: in American English if someone that you don't know were to, say, show up at your house unexpected, you might ask politely "can I help you?" which, with the right tone of voice, is universally understood as a polite code for "who are you and what are you doing here?" What would be the closest equivalent in Spanish? "¿qué se le/te ofrece?" "en qué le puedo ayudar?" or something else?
edit: Ive heard things like "¿en qué puedo servirle?" in a professional context, but I'm specifically wondering about nonprofessional circumstances, like finding someone (innocently) wandering into your yard who might have the wrong address, or is looking for a lost dog, or otherwise generally someone being where you wouldn't expect them to be or don't know why they're there, and you want to question them and find out what's going on immediately, but giving them the benefit of the doubt and not being rude.