Most DM marketing advice is email marketing advice with the nouns swapped. It assumes you have a list, that you can send whenever you want, and that the sequence is the strategy.
None of that is true here. You cannot message someone who has not messaged you. When they do message you, you get 24 hours from their most recent message, and comments give you 7 days. Every tactic below is downstream of those two facts, and most of them assume you have already got people writing to you, which is its own piece of work.
Answer the question before you do anything else
Somebody asks price? and gets back a paragraph about your brand story with the price in the third sentence. That is a lost sale performed in slow motion.
Lead with the number. Then, if you want, add one line of context. The order matters because the person is deciding in about four seconds whether this thread is worth their attention, and the number is what they came for.
The fastest way to make a DM feel like an ad is to make someone read past the answer to find it.
Speed is the tactic, not a feature of the tactic
The gap between a reply in two minutes and a reply in two hours is not a small difference in conversion. It is a different conversation. At two minutes the person is still on the app, still looking at your post, still in the state of mind that made them ask. At two hours they are somewhere else.
This is the entire argument for automating the repeatable answers. Not volume. Timing.
One ask per thread
A DM that asks the person to check the link, follow the page, and reply with their size is asking for nothing, because three requests read as noise.
Pick the one action that moves them forward. Usually that is a reply, because a reply reopens the 24 hour window and gives you another turn. Sending them off-app to a website ends the conversation and closes your clock.
Write for a phone at arm's length
Two or three lines. No greeting paragraph. The Instagram inbox is not a place where formal register reads as respect, it reads as a template.
Hinglish is fine if that is how you talk. "Bhej dete hain, aaj hi dispatch ho jayega" from a brand that actually talks like that lands better than a translated corporate sentence. From a brand that does not, it reads as costume. Write the way you already write.
Do not open with a link
Links in a first reply do two things. They suppress the reply, because the person leaves. And they read as a broadcast, because broadcasts always contain links.
Answer first. Offer the link in the second message, once they have replied and the window has reset.
Set quiet hours and mean it
An automated reply at 2:40am is legal and unhelpful. It arrives when nobody is reading, it looks unmistakably like a machine, and it burns the freshness of the trigger.
Most of the accounts we see settle on something like 9pm to 8am IST. The replies that would have gone out overnight land in the morning batch instead, which is also when people are most likely to reply.
Cap the hour, especially on a good day
A Reel travels, comments arrive by the hundred, and every one of them triggers a DM. Without an hourly cap that becomes a wall of near-identical messages going out at once, and the spam reports that follow do not care that you used the official API.
A cap turns a spike into a queue. The last person gets their reply forty minutes later instead of never, which is a much better trade than it sounds.
Never answer the same person twice for the same thing
Two triggers overlapping on one person is the most common self-inflicted wound in this category. They comment, they also DM, and they get two versions of the same answer within a minute.
A dedupe rule handles it. In our case it is one of ten checks that run in a fixed order before anything sends, and the first check that fails stops the send with the reason recorded. But the principle applies whatever you use: one person, one trigger, one answer.
Stop automating a thread the moment you join it
If you have replied by hand, the automation should be finished on that conversation. This is the check people appreciate the most after it has saved them once, because the alternative is your thoughtful personal message followed by a canned one.
What DM marketing borrows from email
What actually applies
The one that is not a tactic
Automating replies makes a good offer convert faster. It does not make a weak one convert at all. If your DMs are full of people asking the price and then going quiet, the problem is downstream of speed, and the fastest possible reply just gets you to the silence sooner.
Worth knowing before you attribute a flat month to the wrong thing. The related question of whether AI changes any of this is handled separately, and the short version there is also less flattering than the marketing suggests.