The forum has issues with threads that have deleted posts, hence why your link goes nowhere. One workaround you could try is post a unique phrase at some part of your post, search the thread for the unique phrase and copy the search's url. Then you can use this url instead of your post's number and it will take you to that post.

For example:

PensarenotmightierthanBFGs.

https://www.gog.com/forum/general/gogs_general_trading_thread?search=PensarenotmightierthanBFGs.

Edit: On second thought, it doesn't seem to work as well anymore.

Thanks for the trade!

It still works, you just had a space in your link. Try this:
https://www.gog.com/forum/general/gogs_general_trading_thread?search=PensarenotmightierthanBFGs

You are right. Thanks for the heads-up.