Sail and sale are homophones. I suspect incorrect usage usually occurs by accident or because the writer is more familiar with one word than the other.
- a sheet of material used to catch the wind and move a vessel over water
- a voyage or trip on a ship or boat; to voyage or travel on a ship or boat
- to navigate or control a ship
- to begin a voyage
- something that resembles a sail (in shape or function)
- to move along smoothly and rapidly or with confidence
- the exchange of goods or property for money
- an event or period during which goods are sold at reduced prices
My tip: a sale requires money; a sail requires wind.
- Collins English Dictionary
- Oxford Dictionaries Online