Shemiras Halashon Halachos
Hilchos Lashon Hara chapter 5, section 5 . It is forbidden to say that a person is weak as this can harm him if he is a teacher, for example. One may not say that someone is poor or less wealthy than people think as people will not want to lend him money. A person should not quickly decide that his disparagement is for a positive purpose.
Hilchos Lashon Hara chapter 5, section 6 Lashon hara depends on the person spoken of. Praise for one person may be disparagement for another. For example, if one says of a person who receives financial support that he learns three or four hours a day this is great disparagement. But if one says the same of a working man it is great praise. Similarly, if one says that a poor person spends a certain amount for Shabbos it may be praise but the same of a rich person would be a great disparagement. The same applies to how much a person gives to charity. Regarding how a person treats his workers, what may be praise for a regular person may be disparaging for a distinguished person. In general, as the Rambam says, anything that can cause physical or financial harm or cause a person misery or fear, counts as lashon hara.
Do not make the mistake of claiming that the sages say, "That which you hate do not do to your fellow." What is wrong if I say that someone learns three or four hours a day when I would be happy for someone to say the same of myself, and the same regarding charity or honouring the Shabbos? This is a mistake. The Gemara is referring to whatever you would hate if you were of that person's status. Everything depends on one's circumstances.