The account is the credential
Before anyone reads your comment properly, someone will click your username. What they see there decides how the comment lands: a profile with a year of ordinary participation reads as a person with an opinion; a two-week-old account whose every comment mentions the same domain reads as spam, no matter how well written this particular one is.
So the first work is unglamorous: comment in your subreddits about things that have nothing to do with your product. Answer questions where the answer is a competitor. Say something useful in a thread where there is no possible commercial upside. Two weeks of that buys you years of latitude.
The shape of a comment that works
Answer the question completely, first. If your comment would still be useful with the last sentence deleted, you have got it right. Then, if it is relevant, mention what you built — with the disclosure in the same comment, not in a reply, not in your flair.
Match the register of the room. Subreddits have wildly different tones, and the fastest way to be spotted as an outsider is not what you say but how formal you are while saying it. Read three threads before your first comment in a new sub.
Be specific enough to be checkable. Numbers, limitations, the thing that took you two months to figure out. Vague enthusiasm is what marketing sounds like; specificity is what experience sounds like.
Say where you are not a fit
The single highest-value sentence you can write on Reddit is the one that sends someone to a competitor. "If you need per-seat permissions, we do not do that — [other tool] does. If your problem is the reporting, that is the bit we built."
It works because nobody astroturfing has ever written it. It also filters out the customers who would have churned in a month, which makes it good business as well as good manners.
Disclosure, every time
One line: "Disclosure — I built this." It goes in the comment where you mention the product, every single time, even if you disclosed in the same thread yesterday, even if your username is your product name.
Undisclosed promotion is the accusation that ends threads and gets accounts banned, and it is the one thing you can pre-empt entirely for free. In many subreddits it is also an explicit rule.
Handling criticism in public
Someone will say your product is overpriced, or broken, or that they churned. Answer it, plainly, from your named account, without getting defensive and without a discount code. "That is fair — here is why it costs that, and here is what we are doing about the other thing" is the whole play.
Do not argue with the downvotes, do not litigate the details of a support ticket in public, and never ask anyone to change their vote. A calm answer under a critical comment converts strangers better than any positive review, because everyone reading has seen the alternative.
And answer it early: the complaint that goes unanswered is the one that ranks in Google for your brand name for the next three years.
What gets you downvoted
In rough order of how quickly it happens:
- An opener about how you "work in this space" or "help companies like yours".
- A comment that only exists to mention your product.
- Marketing copy pasted into a comment box, in any form.
- Replying to every thread in the sub the same day you joined it.
- Arguing with a moderator in public. Take it to modmail, politely, once.