Wow its a very good question, you need a lot of willing and good club men!
I believe the first team should be picked on ability, in a successful team this works somewhat as winning keeps a lot of people happy.
When you start losing this changes and people what a way out and often use the paying to field excuse. Imagine you are one of the 4 or 5 core club players and suddenly a established member wants to drop down, meaning you get a member who is clearly not good enough for that standard? You then risk losing the quality as they can go elsewhere and play with better standard of players.
Causes upset in various ways, no easy solution.
Were a club in a period of change so its very relevant to me!
Solutions welcome.