If a video card is faulty... there are a few things that can go wrong with it...
Either the power section of the board has a mos that is not working in parameters, and you change that or whatever part you find faulty.
If on the screen of your computer you get characters that shouldn't be there, or the image is distorted, or the image shows up doubled... then the problem is the video processor, that means that the chip got too hot and over time the bga balls, that make the contact between the chip and the board, cracked and it created an imperfect contact, leading to faulty functioning of the entire video card...
So... if a video card for example has a problem... it can be fixed
the bga balls can be resoldered or replaced, the power components that are damaged can be identified and replaced... so if you have a 300 euro video card... and you can fix it for 100 lets say or even 50, would you change the video card with a new one? or fix it...
And by the way if any electronic equipment is fixed correctly, the same problem wont reaper very soon
Hope i made my point... not everything that is broken needs to be changed... i have fixed video cards from desktops, i have fixed laptops with video problems...
I have heard of people with laptops being told that if they have a problem with a video chip there's nothing to be done but change the motherboard entirely... because even if they try to fix the problem it more than surely will reaper... that will happen if it's not fixed properly...