Janice (not her real name), a friend of mine who owns her own business, needed to have an automobile sign made from a local sign shop that she's been doing business with for the last 9 years. They had a new person working there who quoted her a price of $35 for the sign. Janice verbally agreed and the sign shop person said she would call Janice when the sign was ready.
The next day, the sign shop person called and informed Janice that they would not be able to make the sign for $35 but instead must charge her $65. Janice asked if they would still honor the original price quoted. The sign person promised to ask the owner of the sign shop.
The sign shop person called back and told Janice that the owner of the sign shop would not honor the quoted price. Janice replied, "Fine. I'll take my business elsewhere!" And she did.
By quibbling over $30, the sign shop lost a loyal customer who now is "bad-mouthing" the sign shop to all of her friends within her business network. Was this worth the $30?
If the sign shop had decided to honor the original quoted price, they would have lost $30. However, they likely would have elevated an already loyal customer into a super-loyal cheerleader who would almost certainly tell her business friends about what a great company the sign shop was and how everyone should use them for their sign needs.
And this would have been worth the $30 many times over.