don't you people contact your clients, or check your logs/top to see what is going on instead of just suspending them first?
Unless they are causing server problems, don't suspend/kill the account. check your output and see what is using up all the resources. Possibly a rogue script or something of that nature is usually the culprit.
Work with your clients, don't just suspend their account like they don't even matter. That is the worst piece of advice you could follow is to shoot first and ask questions later unless your other clients are adversely affected and you have no choice of course.
If it turns out they are just growing their business, GREAT! Let them know they are using up a good portion of the resources and give them a choice. Upgrade to high usage pricing categories or move to a dedicated server.