With Door Guard

For a few months, there was this rust on the edge of the door on my left rear side of the car. This door was retrofitted due to an accident earlier and was the only door that showed rust at the edge. There was a warranty that came with the retrofit but excluded rust. So I went to a repair shop and they recommended to install door guards on the car. I decided to install only on the door that showed rust. They quoted around 20 dollars for the job and offered to touch it up but I have to buy my own paint. I bought the paint from the dealership for 9.86 USD and sent the car in for the repair. They filed off the rust, touch up with paint and applied a layer of clear and sealed the edge with a transparent door guard. The door guard is supposed to prevent water droplets with coming in contact with the edge of the door. The final cost: 21.75 USD. There's no warranty to the repair and the manager says it is a band aid repair. It is not a foolproof repair where the whole car door is sand blasted and painted which will come to hundreds of dollars.