If you didn't know, I swore off doughnuts about a month ago.
On my last week before my date with destiny, I hit up a Dunkin' Donuts drive-thru to make my final purchase. I was planning on buying a dozen. The employee asked for my order and I asked if they had any specials. He immediately informed me that two dozen were only $3 more than the $8.99 single dozen. I drove away with two dozen.

The "specials" I was asking about was actually referring to the actual doughnut flavors, but this employee was playing for high stakes. Why sell a single doughnut when you can sell the whole dozen? When someone is agreeable to one fact, you can probably sell them on a few more right on the spot.

People buy your t-shirts for $10? You can probably get $15.
If they agree that your horse can jump over a ditch, tell them the horse can jump the Grand Canyon.
She'll give you a hug? Go for the kiss (at your own risk).

Once you get a person saying "yes," you're in powerful position. There is a possibility you could overplay your hand, sure. If you go into things worrying about that, you won’t sell a damn thing. Ask for the moon, it will surprise you how often you get it.