Even if an interviewer doesn't ask about your finances, it can be pretty clear if you're on the very low end. A person living hand-to-mouth may not be able to afford nice clothes (I remember a time when those $99 suit deals were something I had to plan ahead for!), and what nice clothes they have may be worn out. In most of the US, you'll be showing up to your interview in a car because there's no public transit. Is that car an old beater? That says something.

But mostly it's clothes. If you're having a hard time financially, the interview clothes you have (if any) will likely fit poorly, be worn out, poorly constructed, or all three.

By the way: For anyone who finds themselves in this situation, check out local food banks, churches, and your local DoL office. These groups will typically either have an interview clothing program, or will know of one. Nearly every city in the US--even the small ones--will have some kind of charity like this. If you're having trouble dressing or getting rides for interviews, reach out. It never hurts to ask.