Wsalam,
Keyless cars if its a low mileage you'll hardly get any problems. Yes if its a car with high miles on it you may come across some problems depending on how the car has been used and if any electrical work done properly. Keyless keys for cars are expensive to replace but few things you take care of you wont have any problems. Heat, viberation and water are the common causes of problems as its a ciruit like any other. Try not to drop the key best get silicone cover for it as they are cheap. Most importantly if the car comes with only one key make sure you get a duplicate made as they cost arm and a leg when it comes to getting one. As any other circuit you may across problems with the components. A spare key would get you out of trouble and save you the hassle of a last minute search for a qualified and trained auto locksmith.
As my self being an autolocksmith trade for the past ten years and based in islamabad i am sorry wont be able to recommend anyone in Karachi its a matter of finding someone on OLX maybe. But if you have any concerns regarding the electrical side of the vehicle your most welcome to discuss it as I can guide you in the rite direction.
Its good to have prior knowledge of anything technical getting done as its a less chance that a mechanic or an electrician may rip you off.
Regards
Ismail
-AutoKeys
