When you buy something from a reputable business in California, it is a reasonable expectation that if you return the item unopened the next day along with the original sales receipt, you should get your money back. California Civil Code 1723 was enacted to address such circumstances. Signs such as "all sales are final" are not sufficient.
Imagine these scenarios:
• Staying at the hotel, you've forgotten your phone charger, so you purchased another from a nearby gas station/convenience store and found you didn't need the new one. Then you went to return the item only to be shown an obscure hand-written sign saying "all sales are final." Too bad.
• You are going to a regional veterinary hospital and you purchased a dog leash, only to realize you had a leash in your car. So you see the vet and the next day return the unopened, unused leash along with the purchase receipt, only to be told "all sales are final." Too bad.
• You bought a battery for a smoke alarm for the disabled person you were looking after and stopped at a convenience store/gas station. It was the wrong battery so you came back the next day with the battery in its original unopened packaging and with sales receipt - and were denied a refund.
I imagine that you would feel poorly treated by these establishments and would decide not to patronize them ever again. You would tell as many of your friends and associates as possible not to shop there or buy gas there ever again.
Know your consumer rights and familiarize yourself with California Civil Code 1723 - because a crayon-written sign stating "all sales are final" just doesn't cut it.