agree with les, that's why manufacturers provide small print to limit their warranty to 'reasonable use'
offered a life time warranty on the workmanship
damage to the guitar caused by extreme humidity is unlikely to be the fault of workmanship, I'm pretty sure this could be argued successfully in a small claims court, assuming the type of damage points towards extreme humidity ...where would a court draw the line? ..just because you gave him a lifetime warranty( without detail ) does that allow the customer to play the guitar underwater and still be covered ...I think if it went to court common sense would prevail
That said, going to Thailand shouldn't automatically void the warranty, he might well take measures to keep the humidity at sensible levels...but that will probably involve a case with its own AC( if such a thing exists ) and never taking the guitar out of the case unless in an AC room
I would avoid the courts if possible, rewrite your warranty, & after explaining in great detail how Thailand is the 'humidity fluctuation' capital of the world, tell him signs of humidity damage will void the warranty...so at his own risk, send by email that way you have informed him in writing
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