I once worked for a very wealthy man who owned a production company. He taught me a very valuable life lesson. He said, “The NO you have; the YES maybe you can get.”
Of the thousands of scripts that have been submitted to me, only one or two writers have ever asked for feedback. Now you have to understand, my MO is that if I think the writing good and the project have potential, I will offer feedback unsolicited. Usually a few tips on story tweaks, and suggestions for things that did not work for me. I always preference my feedback with the comment that it is just my opinion and can be taken for what it is worth.
All that said - ASK.
Ask for feedback from everyone you submit to that turns you down. What do you have to lose? You never know, you might get some really valuable insights. I know for the few writers who asked, I responded. Not everyone will, but you already have the “no,” - the nothing. So ask.
If you get enough responses it might help direct your work. It will help you know what is working and what is not. If you get several similar comments you know it is something you need to work on. If the comments are all over the map, then you need to see what resonates.
Now, if you get feedback you don’t like, DON’T ARGUE with the person who was kind enough to take the time to give it. If you don’t like the feedback, if you disagree strongly, then just thank them for taking the time and toss it over your shoulder.
Another nice thing to do is to send a thank you card if you are able to get their address. Notice I said card and not email. Not many people send thank you cards any more. This will make you stand out. It does not cost that much and may make a huge difference when you want to pitch that person another project.
If you don’t have their address, ask for it.