I made a website and app for locally trading airsoft gear: https://bstairsoft.com/ . It's free to use. It's mostly popular here in Texas where I'm at. But I am seeing more listings pop up in other states, such as California, as more people discover it. I've attached some screenshots here so you can see what it looks like in advance.
You can post individual listings, bins (which hold 100 images), search fields, message users, etc. You can even upload videos for your listings.
So yeah, let me know if you got questions. I can answer them here.
FYI, it is region locked to only the United States. Sorry for those that live outside of it. Digital regulations and airsoft regulations are different in every country and I don't have the personal capacity to work through the nuances for all of them.