Lots of different possible scenarios here, but this is a super common thing in business.

A couple of pointers:

1) Make sure you understand what they really want. It is common for a person to ask "can your hardware run on 12V", for example. But what they really want to know is something like "can I use this on my solar powered RV that will be parked in a 122F desert". This is just one of a billion examples from my career. You need to determine things like do they mean a stable 12.000V from a power supply, or a really variable 12VDC vehicle system that can range from 11-15V commonly. And then there is the whole ruggedness of the hardware issue. You need to be able to look ahead a bit and often assume the person isn't really asking the question they want an answer to.

2) The best way to be successful in business is to predict the future :) By this I mean determine how to set achievable expectations. If you feel confident that you can get an answer by COB, then state that and do it (predict the future, make it come true).

3) Communicate commitment and honesty. It is ok to tell someone you don't know, but you can say this in a lot of ways. Depending on all the variables, saying something like "this seems possible, but I need to check with X", or "I believe we did something similar for another situation, let me get more data internally and get back to you by tomorrow morning", etc.

If you want to setup a coaching session I'm happy to do a 30 minute zoom/whatever.

Heh your oddly specific example in point 1 makes me smile. I'll just add "can it handle a voltage spike up to 60V for a second or two in the event of a load dump?" to the list of questions hidden in "can your hardware run on 12V?"