A commercial post is where the seller is not a private individual and is operating as a company, sole trader etc and those who regularly sell via the likes of eBay etc. However, these guidelines may also add value to all sellers posts.
You are welcome to post stock lists; fishes and anything else within the forum rules. However, you are more likely to annoy than attract customers unless you do it well! Here are some guidelines on best practice.
Introduce yourself! This is really the golden rule if you are to be successful. It's frowned upon by forum mods and will not get you a great deal of custom if you just dive in with a "buy from me" post especially if its a simple link to another site. I most folks aren't particularly technical, but, from a technical standpoint this is not nice behaviour. Without an introduction, and certainly if not right on topic, it's close to spamming.
People will follow (subscribe) to your thread. Therefore, and to stop too many threads from one entity, I would ask you to keep all the posts in one thread, say call it "Acme Fish Store Stock" and keep updating it with new posts as new things become available. Lots and lots of threads with one post is not appreciated/good by the site or your customers.
Adding your own pics of the fish is good. Adding pics of the species taken by someone else is a very good way to turn folks off and may be illegal! Bear in mind using an image without permission to make profit is pretty poor show, and not the same as posting it in a non-commercial discussion.
You should post prices, but be prepared to discuss them either openly or by pm. That's up to you.
Check the names and learn how to use the clog tag feature to link to the species - that WILL get you kudos. e.g. L034 or Blue Catfish or Corydoras trilineatus. Correctly ID'ed fish will get you noticed. Just regurgitating trade names is a good way to demonstrate a lack of understanding.
Also, be prepared you will get all sorts of questions - but then you work in a shop - you will be used to that! The team will moderate if required, but you are putting yourself out there (and gaining the benefits of doing so) but you may need to publicly defend a position.
Dyed or injected fish will get you quick scorn. Hybrids are also a hot topic and selling them may also give you a hard time or just switch people off a bit.
If in doubt ask either by PM to me or by replying to this thread. You may also wish to PM me prior to your first post and thus be able to preface that post with "posted with permission". It is good for others to know you were kind enough to ask first!