With me it was dependent upon how many times I had seen them in the ER that month. If it was their 20th visit for HA, backache, abd pain, etc. I would say, "On a scale of 0-10 with 0 being no pain and 10 feeling like you were ran over by a semi truck and then lit on fire, how would you rate your pain?"
If they responded "15" or whatever number above 10, I would say to them, "I'm sorry sir/madam, but 15 does not fall between 0-10."
Honestly, I think the whole 0-10 numerical pain scale is ridiculous. A lot of people don't understand it. And then there are people like myself, who could have tears running down their face and not able to stand up straight because they hurt so bad that would still rate their pain as a "1 or 2".
I worked in an ER that used a behavioral/non-verbal pain scale for adults and it worked a lot better than a numerical scale.