is 145k too much on a 2011 checy malibu? its a 4 cylinder and it had something put in it called 02 sensor. i havent bought it yet but have been considering it and this would be my first car ever

No its not reliable, too much to pay anyway, maybe $1700 going on 8 yrs old. Look for a good Toyota or Honda.

Most time when a o2 code comes up that is not the problem their will be another issue causing it to run lean or rich, the code for o2 just means there is a issue and seller does not want to figure it out or pay to have the work done, which means it may leaky intake or head gaskets or bad fuel injectors, bad valve seals ect. There is a reason the o2 code set and at 145k its not the sensor, the sensor in the exhaust is just reporting there is something wrong. Stay away, Let him put a o2 in it and the light will come back, may take a few days so do not be fooled.