Life skills: Dealing with a customer service issue

When they screw up

• Be calm, but firm.  This is hard for me when I get frustrated, but pissing off the customer service rep will only hurt you in the end.  If they stick to their script, stick to yours: "This isn't right, and I expect to be compensated/reimbursed/credited."  It never hurts to show your allegiance as a customer, so they know that you're worth pleasing: "I love your company and shop with/do business with you guys all the time, but this left me really disappointed."
• Don't waste your time with someone who doesn't have the power to give you want you want.  If you don't make progress with the first person you talk to, say "This is a serious issue, I'd rather discuss it with a manager.  Can you transfer me, please?"  You can even call and ask to speak with a manager directly.  You may hold for a few minutes, but it saves you the hassle of telling your story over and over.
• Remember that it is much cheaper to keep a customer than find a customer.  There is always something they can do.  Insist until you get an outcome that you like.  This website suggests you simply hang up and call again if you're not getting the answer you want.  Fees can always be reversed, items can always be exchanged, and credits or comped items can always be granted.  Don't settle for "there's nothing we can do."  There's always something, so obviously you just haven't found the right solution.  Say: "I understand you may not be able to do [X], but there has to be a way for you to make this situation right.  What's your suggestion for how to fix this problem?"

When you screw up

• They still want to keep you as a customer, so you can still win this.  Technically, taking the above tactic and insisting it was their fault could still work, but this isn't my style.  Instead, simply owning up, but making it clear that they should accommodate you, can get the payoff you want with your scruples intact.
• Don't go into too many details about what you did wrong, focus on what happened, and what they can do to help.  "I didn't get my bill.  Unfortunately, I've been charged a late fee.  This is the first time this has happened to me, so I was hoping you could remove the charge.  I'd really appreciate it."  You can pretty much always get a first-time or first-in-a-year late charge reversed on a credit card or store card.  For other situations, many stores or businesses will accommodate you if you show your willingness to work with them.  For example, they might not be able to give you a refund for something you washed on the wrong setting, but they can certainly exchange it for the same item.
• If they don't give in, note that you are a reliable customer, and that using their company won't be sustainable for you if the situation isn't resolved.  "I'm sorry, but I can't afford this extra charge/to buy a replacement item/to pay the current rate.  If you can help, I'll be able to keep using [company] in the future."

Another thing that can be maddening about the customer service experience is trying to get an actual person on the phone.  Especially when there's no 800 number, and the entire experience is eating up your minutes.  My personal tact is to hit 0 or say "agent" until a person comes on the line, but if you want more specific advice, the website "Get Human" has tips for numbers and codes for individual companies to get directly to a representative.

Anyone else have good tips for getting your way with customer service reps?  Or, better yet, is anyone in the business and have some inside dish on what customer tactics yield results?