I did some touch ups on my car with cans, from paint peel on bonnet and scrape on bumper. It's all in the prep before you put on the colour coat.
For the bumper I sanded back all around the area, back to the black plastic for most of it. Used a plastic primer which adheres to bumpers and the like. Mask off the surrounding panels, don't mask off halfway through a panel as you might get unsightly lines. Don't forget the wheels and tyres too they may be overspray range.
Filled scrape with a filler, sanded, filled, sanded, filled. Primed, primed more, used primer filler, more and more.
Sanded with fine 800 grit, sand more, prime more, sand more maybe 1200-1500 grit.
You end up sanding and painting a much bigger area than what the original scratch was.
Then once I had smooth and primed surface, cleaned with wax and grease remover I applied the colour coats as per can instructions for the colour matched paint.
Then I applied clearcoats as per can instructions. Clearcoat was orange peel finish.
So I waited 2 days, sanded it back with 1500/2000 wet paper, until the orange peel was gone, but not so much that you cut through the clearcoat.
I then got a a rotary polisher, wool mitt, with some meguiars ultimate compound and the fine scratches and dull finish left from the 2000 grit sandpaper came out nicely.
Outcome, was quite good I think being my first go at it. I only did it because it was going to be very expensive to get it professionally done, and the car isn't worth much anyway, and it looks better than what it was. But if you have a nice car with low km's etc then it may be more worthwhile to let the professionals do it.