"... Would you like a house salad for 99 cents?"
"... An extended warranty is only $9.95!"
"... We have a special on the NFL package..."
"... Wanna super-size that?"

You're already in the store or on the phone with the salesperson, so this is easy pickin' for them! They'll upsell you until the cows come home, because it's never easier to sell to someone than when they're ready to buy, and guess who's buying?

MBH: "I'd like to send this Printed Matter rate, please."

USPS:"Priority Mail is $10.95, and First Class is $5.50."

MBH: "No, Printed Matter rate, please."

USPS:"Tracking or delivery confirmation on this?"

MBH: "No, thank you."

USPS:"Insurance?"

MBH: "No, thank you. It's worth only a dollar."

USPS:"How about some stamps?"

MBH: "No, I still have Christmas stamps, thanks."

They upsold me four times! The post office, for goodness' sake! I expect a salesperson to try to sell me lots of stuff I don't need, but Mr. McFeely? Give me a break! Speedy delivery that!

• Realize upselling for what it is. Most people either want (a) to make as much money as they can or (b) to keep their job, so they make as much money as they can for their employer. As competitive as business is, sellers have no choice, really.
• Just say no! Your wallet will be proud of you.
• Ask if something offered is free or not. Restaurants are notorious for this. The feta cheese the waiter "offered" to put on that salad may cost you, but they may not come out and tell you that if it's listed as an extra in the menu.
• Gently train people you deal with regularly by being clear that you won't be upsold. They may just quit trying. (Or they may get sneakier about upselling to you. But that's part of the game!)
• Come back with something that doesn't cost anything. "Would you like something to drink with that?" might be countered with "Yeah, I'd like some water, please."