buy market car only and avoid avoid out of market cars. in karachi the market cars that are sure shot quick sell are:
Corolla (all models of 1300cc xli/gli - esp 2009-new)
Mehran - buy newer models
Cultus old model esp efi one
WagonR (hot cake for Uber/Careem aspirants)
avoid JDMs in initial stage of your work
avoid cars with legal issues like missed plates, engine changed, file lost, duplicate papers etc
i suggest to gain some expertise first of knowing how a good car looks like - e.g. paint condition, interior, engine area. best is to invest in a smaller car at first e.g buy a good efi cultus 2009/10 model and try your luck on it. if you really feel that you can do it, then move forward for cars like Corolla with bigger investments and bigger profit margins. even if you roll over 2 to 3 cars per month then you have a sizable income generated - but neeyat achi rakhni sab se zaroori hai aur sabr rakhna hai kyu k aise aise buyer aatay hain jaise aap ne chori ki car rakhi hui hai. i have done this work on very small level in the past and achieved very good results..this is all my own experience and others can definitely have differences.