"I stood firm and argued that charging $100 for reading data on a laptop that took less than three minutes was unethical and wrong," Clark wrote on my Facebook page. "I told them I was coming to get the car. A few minutes later, I received a call informing me that they were waiving the $100 laptop data reading charge."
3. Medical bills
A young newlywed on his honeymoon was bitten by a rattlesnake and wound up with a $20,000 hospital bill. When the uninsured man talked to a hospital representative about it, she told him the only alternatives were to pay in full and get a 10% discount, agree to a $550-a-month payment plan for the next three years (which he and his wife couldn't afford, given their $24,000 annual income), or file for bankruptcy.
In fact, I told him, he probably had several other options, because medical bills are a lot like sticker prices for cars. Few people pay the posted prices.
If you're low-income and have a hospital bill, you should ask to speak to the hospital's financial counselor. Many hospitals and other medical providers have charity programs that provide discounts for people making up to 300% of the federal poverty level. Since that level is about $14,000 for a family of two, a couple making up to $42,000 might qualify for some kind of break.
Another option is to ask for the same discounts the medical provider gives major health insurers. These big insurers negotiate substantially lower prices -- 30% to 70% off the sticker prices.
You also should scan any hospital or medical bill for mistakes. People regularly get charged for drugs, treatments and procedures they didn't receive, often at highly inflated prices. Medical Billing Advocates of America, whose members help patients review their bills, says 80% of medical bills contain errors. Consumer Reports offers more details about what you should look for.
Finally, avoid taking out a loan or using a credit card to pay medical bills. Once you've done that, you've lost all negotiating leverage, since the provider has its money. If you can't pay all at once, ask for a payment plan. Many providers offer these at zero interest, while loans from other sources can carry sky-high rates.
4. Mattresses
Shopping for a car is easy compared with shopping for a mattress. The same model car doesn't go by different names with slightly different features at different dealerships, but mattresses typically do. Manufacturers and retailers deliberately obscure the information you'd need to compare apples to apples.
Consumer Reports, which provides tons of research on cars, doesn't venture to provide ratings for mattresses "because of the role played by personal preference and the fact that different store chains typically do not have the same models," according to its website.
So that means you have to do a lot of schlepping around from store to store and lie on a lot of beds to figure out which one works for you. But you should know that Consumer Reports typically paid half or less of the list price for most of the mattresses it bought for testing (and dissection). The exceptions were a Select Comfort Sleep Number bed, on which it wrangled just a 12.5% discount, and a Tempur-Pedic bed, which typically offers no discount but may offer some freebies, such as free delivery or a free pillow.
5. Jewelry
Markups of 100% or more are common in the jewelry trade, and even national chains have some wiggle room in their prices -- although you probably can bargain harder with independent stores.
Last year while on vacation, I spotted a lovely sapphire-and-diamond ring in a shop that sold estate jewelry. The smart saleswoman had me put it on; she knew that once you touch something, you're more likely to buy it.
I offered half the amount on the price tag, and we started bargaining from there. I kept taking off the ring and saying it was too expensive; she kept urging me to put it back on. Eventually, we agreed to a price that was a little less than halfway between the original price tag and what I offered to pay.
And I overpaid, according to a later appraisal that put its value at 61% of the sticker price. If I had to do the negotiations again, I'd start lower -- maybe 35% or 40% of the list price, and go from there.
I also should have left the shop at some point. As with a home or a car, you'll often get the best deal if you're willing to walk away.
Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.