For those Jedi Knights of the spray gun runs are just something that other people get, for us mere mortals they are an occupational hazard of waving a spray gun around in the hope of laying down a good finish on a panel.
As I definately fall into the latter I managed to get some runs in a door I was painting, mainly due to not allowing enough time between coats I suspect.
The door started looking like this, the run was about 8" long and while hard to photo was huge.
First thing when you get a run is don't panic, don't try and do anything about it while its wet as you will probably make it worse. Once its fully dried and hardened (noting that this may take longer than usual as the run is going to be thicker and hence take longer time to dry) you can start trying to extradate yourself from this mess. At this point you have two choices, sand the panel down and repaint or try and get rid of the run.
Generally you don't have anythijng to lose by trying to get rid of the run as if it works great and if not you are into repainting anyway. The big problem is that if you just try and block the run out a lot of the time you will sand through the surrounding area before you get anywhere near removing the run. I've tried run razors and never had much luck with them, generally just making it worse.
My weapon of choice is a nib file like this: www.ebay.co.uk/itm/364323173140?hash=item54d35a7314:g:T1sAAOSw~mRkmtGc&amdata=enc%3AAQAIAAAAwCYZz9MYU1Bkwawifu6uModJSEA9TdyXbIFlvr23YgJNIURiESkSSZ44OXVp3qY6MdZJSre5gwWMY0WKLEsrEmO1%2BLKwYlSLJv0kJiUAXf53L1ZXaF4nZrGa%2BWSrbbeCJYE3npA8FYtl2X5BbwWzTMkrIxZeG5IxvrPGkhg4PkV7Vmq06kOHEyLHWLEoOGdyJ2Uyqjeso%2Fb0vNO3DIsDJgZOXbzxwLcv2qa1ifHyy7dfuQtaxdRndxa8%2B6SWAJ9O%2FA%3D%3D%7Ctkp%3ABk9SR_yoltnTYg
First task on my door was to remove the run by carefully drawing the file along the run, you can see the main run here and also a smaller one below it:
Once the run is gone you then sand the whole panel/area over as you would for colour sanding, I used some 1500 grit wet and dry used wet on a block.
Then I ran over the door with a 3000 grit Trizac disc on my DA sander (used with a small amount of water) which gets most of the shine back:
Finally a good compounding with the polishing mop and you can't tell that it was painted by a complete chump!
One thing to note is that in some instances i've had runs where the pigment has seperated out and thefore although you can get rid of the run the paint is a different colour, depending on how bad it is you can either live with it or repaint.