Pakistan is large county with million vehicles, and in Pakistan there is no proper way to buy & sell cars etc, just peoples using a simple paper for buying Vehicles and in result there many frauds and buyer lose a big money.
For buying a vehicle you should be aware that who is the owner but sometimes its hard if your away from a Excise and Taxation Office. Excise and Taxation Department of Sindh has launched an online portal for verification of vehicles in Sindh, including Karachi.
For Online Verification visit this site
Just enter Registration No of your car/vehicle and you will see sufficient information about your vehicle but some info will be remain in private to protect the owners.
You also can verify Punjab registered vehicles online ,Visit.