People who have strong interests, passions, hobbies etc. My mum was very hard to buy for. She didn't like perfume, makeup, jewellery etc. She loved sentimental gifts though, so I had to try and think of something every occasion which got more difficult over the years.
My sister is very difficult. She doesn't have any hobbies or interests, she doesn't read or watch films etc. She usually gets perfume and clothes from her partner and I usually try to think of something different/personal or buy her perfume as well.
I'm very easy to buy for, everyone says this 😂 I love music, art, tech, gaming. I collect Disney mugs, vinyl and funko pops. I love lego and books, obsessed with Harry Potter, LOTR etc. I also like makeup, weird jewellery, chocolates. I love throw blankets and stationery. My dh is also quite easy, he loves rugby, music, cars, whiskey, comics, lego etc.
So I think if someone likes a lot of different things it makes it quite easy to buy a gift for them, but some people are more restricted in their interests. Sometimes the best thing in these situations is something personal (if you know what they'd like) or a gift card and some chocolates.