Hi, Marco! Welcome to the THF forums! I'm not an expert in this area, but from the pictures you've posted, it looks like the cracks are just the seams where the pieces of sheet rock meet and the paint is cracking from shoddy taping and bedding work before the wall was painted. Usually, people place molding around the ceiling/walls and baseboards around the floor to cover those areas, because it's hard to get a really tight fit between the walls and the ceiling or or flooring. I noticed that there was no molding showing in these photos. And from the photo of the center of the wall, it seems to be about where the two sheets of sheet rock would normally come together when building the wall. When a wall is made of sheet rock, they place one sheet of sheet rock above the other one, as closely as they can get it to fit. Then they cover the gap in the seam with putty and/or paper tape. Afterward, they paint the entire wall. But it's hard to get the paper and putty to smooth out level with the rest of the wall's surface, and if not done correctly, the paint will crack where the seams are. Some people fix this problem by putting up paneling instead of just leaving a painted surface. Other people fix it by filling in the cracks with putty, glue, toothpaste or paint and then sanding it until it's smoothed out and blends in with the rest of the wall. And some others will fix it by putting up a a wood or wallpaper decorative border.
Also, one of the cracks you showed just looks like it is where the paint dripped and made a "run" or raised ridge. Whenever it's too noticeable, house painters normally sand these runs until they are as smooth as the rest of the painted surface.
But unless someone with more experience inspects it in person, it's really hard to tell what might be causing the cracks just from looking at the photos. So definitely get a professional house inspector to check out the entire house for you before purchasing one. And make sure it's an inspector that is working directly for you and not being paid by any other party. There's a huge difference in what type of inspection is done and what kind of information is shared with you.
What type of foundation does the house have? Has it ever had any roof damage? Is the home located in an earthquake area? Does the ground shift frequently or get soaked by rain or other sources of water? What kind of flooring does it have? All of these factors can determine the cause of the cracks.