Luckily most paint manufacturers are now offering warranties on their exterior paint, and the warranty is stated on the paint can. I use it as an indicator of how long they expect their paint to last. There is a similarity to all the warranties in that they only cover the cost of the paint, and the quantity needed to repaint the affected area. So although the act of offering a warranty sounds reassuring, it requires record keeping by the customer, and all they give you is another gallon of paint which does not cost them much.
The warranties state specifically that the paint is warrantied not to peel from the immediate surface to which it is applied, and not to wear through to the to the underlying substrate due to natural weathering. Physical abrasion is excluded as well as improper preparation.
I warranty that the paint I apply will not peel from the immediate surface to which it is applied for one year.
What is not warrantied: peeling of underlying coatings beneath the surface to which I painted; construction defects which allow moisture to penetrate; freestanding structures which allow moisture penetration from multiple surfaces such as decks, arbors, fences; stains bleeding through the coating which appear later in time; chalking paint; color fading; products specified by the customer which are different than I specify; and transparent coatings such as deck stains.