I have much more sympathies for 'extreme programming' than for 'agile'. Mostly because I see many more clueless people use 'agile', while 'extreme programming' seems to be a term that time forgot and eg http://www.extremeprogramming.org/ is still in a state of relative innocence. The website was apparently last updated in 2009.
My experience is that invariably results in "development by veto". Each prototype they say that's not what I want, give me something else (that I'll fail to describe just like the last time) and I'll tell you that is wrong too after you've worked on it for a few weeks.
Occasionally, you'll randomly get something they accept - but only for a few weeks until they come across some missing capability for some other thing they never told you about.
> My experience is that invariably results in "development by veto".
Yes, I wasn't entirely serious.
Though you can get pretty far by doing some roleplay, where you pretend to be the computer/system (perhaps put up paper screen to make it easier to roleplay, and pass messages written on paper) and have the expert interact.
You still have to actually listen to the complaints. "That's not what I want" does not mean try again, it means they have no interest in what you are trying to offer in even the most basic sense. The lesson from that type of complaint is that you are barking up the wrong tree. Time to move on to something else.
When you are solving a real problem, you will still receive complaints, but they will be much more constructive.
Or you give them a prototype of the program, and see what they complain about?