Is it permissible to write good about a product in an advertisement?
Yes, as you want to sell goods it absolutely permissible to do so. But if there is any defect you are obliged to let them know so to save them from the harm, as it is in the western countries, we find this practice mentioning the side effects of the medicines or the precaution age for the toy etc. So, this is from the Islamic principles that you have to add the information regarding the harm which may occur with the usage.
Prophet Muhammad (ﷺ) is reported to have said:
“The buyer and the seller have the right to keep or return goods as long as they have not parted. If both parties speak the truth and point out the defects and qualities, then they will be blessed in their transaction. But if they tell lies or hide something, then the blessing of their transaction will be destroyed.” 
 [Bukhari, Book 3, Volume 34, Hadith 327]< Back to Questions