Has the soil been checked recently for excessive/defficient levels of nitrogen/etc (due to applying too much fertilizer), excessive levels of salt or soil pH too low (too acidic)? Can you ask what has been done to the plant or what has happened near the plant lately? To put things in perspective, do you know where is he located (city, country, USDA Zone if applicable)?

Sorry. I left out a paragraph with a link.

Also have your friend keep an eye for bumps on the underside of leaves. These bumps are caused by too much watering and the bumps are plant cells basically exploding due to too much water. The problem is called oedema. The link which follows has nice pictures of many leaf problems: http://www.camellia.org.au/UserFiles/file/Pest%20&%20Diseases_Final.pdf