How can high profits be determined in selling without falling into ghubn (gross deception/exploitation), and does a customer's trust permit raising the price on them, and is it permissible to change prices without reason or due to forgetfulness?

There is no specific percentage for profit that merchants must adhere to. Rather, it depends on the circumstances of the trade, the merchants, and the goods, while observing Islamic etiquettes. Slight deception by the seller towards the buyer has no effect. However, excessive deception ranges between being disliked and forbidden, and it grants the buyer the option (to cancel the transaction). If the buyer was ignorant of the value and sought the seller's advice, then the seller's deception is a forbidden fraud that necessitates the option (for the buyer). But if the buyer did not seek the seller's advice and the seller did not deceive him, then it is not forbidden.