Guarantees?

[lilenth.livejournal.com]

There's been a fair few posts on Terms of service and other legal bits that artists need to take commissions, but what about afterwards? I'm sure many people have many happy customers who have enjoyed their work for years but there's always a chance that something will have gone wrong with something after it's completed.

How long a guarantee should an artwork have on it? How long after purchase would you expect an artist to compensate you/replace/repair/refund if your purchase turns out to have a fault? (By fault, I mean an actual fault, ie it falls apart or fades suddenly for no apparent reason, not "waahh that stud is a millimeter off, it's ruined")

What sort of things would you consider an artist has to cover, what would definitely not fall under it in your opinion?

Is it strange to guarantee something like an illustration?