Depends on your definition of cheap and quality. Generally speaking used business machines tend to be the best value for money

Can’t speak to the build quality but those specs are more than adequate for web browsing.

Replace the battery, do it now, this shit can start a fire.

Most business machines (Lenovo ThinkPads, dell latitude, hp probook) will allow you to spec them out as you wish if you order directly from the manufacturer. Playing around on lenovos website you can get an e14 or e16 with a Ryzen 7 and 40gb of ram for under 800 but it’s a zen 3 Ryzen.

Yes people buy laptops in every state of disrepair but you will get significantly less for it.

That really depends on you. The vast majority of your work can be achieved on a much cheaper machine, yes even data science, the lecturers know not everyone has powerful hardware and tend to factor that into their assignments and for the event that you can’t the lab at uni or online services like Google Collab are available to you. If you want a Mac but don’t want to spend that much maybe go for air.

he said it Can easily be fixed for free

That’s bs, if that was the case he would have done that before selling it.

Sounds like something sticky was spilled on it but that’s not the only possible explanation.

Windows has a feature where when you press shutdown it won’t actually shutdown it will just close any apps that are running and suspend itself but sometimes for one reason or another it can’t do that so it will actually shut down. This is most likely what’s happening.

The intel+Nvidia option will be more performant but a dedicated GPU will use more power.