Everyone have a different scent of perfume they prefer that is why you have to think a lot before you buy a perfume for someone, take your time to choose a perfume for someone else that may let you have a chance to buy the perfume that the person will like. There are three tip I can give in how to buy someone a perfume.
1- Look at her style:
How person dress can tell you a lot about the perfume scent they would like. If the person like to wear dark colors they are more probably would like to have darker fragrance but if they have elegant look they might want rose scent, it depend on the way they dress
2-work by process of elimination:
It is hard to choose a perfume for someone because you do know exactly what that person will like but you might know what kind of smell of perfume they think is good to have, so the best thing to do is to eliminate the perfume that you think that person will not like such as strong scents or kind of flower they do not like. Try to focus in the smells that you believe that person will like and eliminate everything you think he will not like.
3-Follow the brand:
If you know what brand of perfume she or he likes than buy it because it will save you a lot of time and the probability your friend will not like is very low. Even if you think it is expensive to buy a brand bottle perfume for a friend but remember that your friend without doubt she will like it and be thankful to you.