The rust problem is VERY bad. It's not just about the looks and feel of the vehicle but the overall security of the people who are riding that vehicle in a major accident. Rusty car will most probably bend everyone in half in a major accident. The reason for this rust problem in comparatively new and less driven cars is primarily due to PIG-3 not galvanizing the hidden metal surfaces of their vehicles in Pakistan, especially the inner surface of the frame in order to save a few bucks. No matter how new a car is, if it is rusty then stay away from it. Just a month back, I saw a brand new Mehran that was only driven for one month out of the showroom and the customer had to bring it to the workshop to take care of rusted side panels as the paint was ballooning out everywhere on the underside.
I've rust proofed my car by covering it with Rustoleum's Rubberized Undercoating. My car looks flat black from the underside as well as under the carpet. I don't give a damn about the resale value going down because for me, my family's safety and well being comes before the car's looks from the underside and under the carpet.