I tried to use in-game mechanic by selling items in player trading machin that is located in trader P1. I wanted to sell Lead and "machine" did buy almost all of it, there was 7 left so I wanted to take it out. It did let me take it from machine but there was -3 left, I did leave it for around one in-game day and when I check it out again there was around 66 000 Lead that I could take out. I tried it again just to make sure and it did that again. I don't know if it is possible to do it with other traders outposts.
Pastebin link with logs: