Is this $45 Giant OCR 3 a steal or a trap?

Hey everyone, I’m looking for a casual ride for city tracks and found a Giant OCR 3 for $45 aud.

It's been marked down from $100 and seems to have been listed for a while. The seller says it needs a service and the gears are clunky – possibly needing a new cable.

I know it’s a cheap bike, but I’m on a budget and don't want to buy something that's going to cost me more in repairs than the bike itself and I’m also not very experienced with mechanical fixes. I’m planning to paint it black and use it for casual rides a few times a week.

I have a few questions…

-What hidden costs or red flags do the pros here see that I might be missing?

-For a total beginner, is a gear cable actually an easy fix?

-Would the frame size be right for me because getting it too long or short can cause backpain? (Im 171cm)

-Coming from flat handle bars, are these hard to adapt/do you get backpain?

Thanks for the help!