It sounds like they want a representative sample, which isn’t something I’d be confident in my ability to help them with directly, so I’d advise them to first scan for a person who’s very experienced in statistical sampling and to then work with that person to determine a strategy that will meet their goals.
If they weren’t on board with that plan, then I’d see if they were willing to share their target sample size. If I didn’t have an option for the count I would assume they would be contacting 1% of the population (80 million people). I’d also let them know that being representative and selecting for traits that will make encounters go smoothly are conflicting goals, so I’m prioritizing for representation and they can figure out the “please don’t pull a shotgun out, human!” trait on their own. Depending on all that, I’d recommend an approach that accounted for as much of the following as possible.
- gender (male, female, non-binary)
- race
- culture and sub-culture (so this would include everything from religion to music to hobbies)
- profession
- age, broken down into micro-generations
- mix of neurotypical and neurodivergent
- different varieties of neurodivergence
- range of intelligences