What would you do if you really liked an admin and knew they were the right person for the job, but they ask why they should do it, meaning what will they gain being admin? Please help me. 🙂
If they aren't on your forum, or isn't a staff on your forum then I wouldn't bother asking. Personally, I find it disrespectful to your community if you find someone to be admin from another forum. They probably wouldn't even know your forum, or even know how it operates. Giving them that top job would definitely make you lose members.
If it's staff on your forum, then ask them if they would like a promotion. Not everyone has the time to work for an online forum, so let it be if they decline. You can't force people to become an administrator.
Also, there are always faults. There isn't a such thing as "right person for the job". Only you are the right person for the job as you know what you like and want for your forum.