When advertising a business there is a lot of information that can be left out, to help persuade the consumer to purchase the product/service. For example, a bottle of yogurt can say “80% fat free” which actually also means there’s “20% fat”. They advertise in a way to manipulate the persons emotions to make the sale. Or another example is a company might say, “this stock can make you $1,000 in 1 day”. Technically any stock can make that type of profit in one day.

Or another example is you make the person feel like they are going to lose weight with your product but you never actually guarantee anything, you just lead them to believe it with advertising.

People will buy things based on how they feel.

Is there specific islamic rules you have to follow when advertising? At what point does it become unethical/haram?

Any way of cheating is haram but putting attractive things ahead may not be haram. Misinformation or lying is forbidden