The promises the law reads into a sale whether or not anyone wrote them down, and the federal act that limits how a seller can take them away.
Every state's sales law implies two warranties into most sales of goods by a merchant. The implied warranty of merchantability is the promise that goods are fit for the ordinary purposes such goods serve - a refrigerator keeps food cold, a car runs. The implied warranty of fitness for a particular purpose arises when the buyer relies on the seller to choose goods for a specific need the seller knows about. Neither requires a written warranty, a receipt that mentions them, or any promise by the seller at all.
Sellers can exclude implied warranties, and "as is" or "with all faults" is the language that ordinarily does it, provided the exclusion is conspicuous. That is why the words matter on a used-car window sticker or a second-hand sale: they are not a description, they are the removal of a legal right.
Federal law steps in where a written warranty is offered. Under the Magnuson-Moss Warranty Act a seller who gives a written warranty on a consumer product cannot disclaim the implied warranties at all, may only limit their duration to that of the written warranty, and must label the warranty "full" or "limited" and state its terms clearly. The Act also lets a consumer who wins a warranty claim recover attorney's fees, which is what makes small warranty claims worth bringing.
Before buying, the question is whether the sale is "as is" and what that removes. After a failure, a lawyer can tell you whether the implied warranty survived, whether the written warranty's exclusions are enforceable, and whether the claim is one where fees can be recovered - which changes whether a claim over a few thousand dollars is worth anyone's time, including the seller's.
Choose your state. Each link opens the directory page for the city in that state with the most currently published law firms in this practice area; a +n beside the city is how many other cities in the state also have one. The list is generated when this page loads, so a state whose listings have lapsed drops out rather than becoming a dead link.