Everyone is at a different level in their photo/video journey. You were once new to this game as well, so consider that when posting and commenting. Be helpful, don't be a dick.
Posting photos or videos for feedback and critique is fine. However, if you post content here and then are absent from the conversation in the comments we'll assume you're doing it for clicks and your post will be removed. It's your post, stay engaged!
Affiliate links are okay provided the product is relevant to the community. You must disclose that the link is affiliate.
If you are posting to promote your blog, your youtube channel, your... whatever and that post contains no other content that offers value to the community it will be considered spam and removed. Do it too many times and you'll be removed.
There are countless places on Reddit to buy and sell used gear, so let's not add another. If you don't know where to find used gear you can ask that question, but don't post your gear here or your request for used gear.