Most small retail shops in India do not get GST wrong because the rules are hard — they get it wrong because the billing setup was never configured properly on day one. A few minutes spent getting the basics right saves hours of correction later, and keeps your accountant happy at filing time.
1. Confirm your GST registration status first
Before anything else, settle whether the business is actually GST-registered. If it is, every invoice needs a valid GSTIN, the correct tax breakup and a "Tax Invoice" heading. If it is not registered — common for very small shops under the threshold — invoices should say "Bill of Supply" and must not show any tax breakup at all. Mixing the two up is one of the most common billing mistakes we see, and it is entirely avoidable with one setting decided upfront.
2. Set tax rates at the category level, not per product
Typing a GST rate into every single product listing does not scale, and it is where inconsistent rates creep in — the same category of goods ending up taxed differently just because someone typed 12 instead of 18 on one item. Set a default tax rate per product category instead, so every new product in that category inherits the correct rate automatically, and only override it on the rare product that genuinely differs.
3. Decide inclusive vs. exclusive pricing once, deliberately
Whether your shelf/menu prices already include tax ("inclusive") or tax is added at checkout ("exclusive") should be a conscious business decision, not whatever the software defaulted to. Retail shops serving walk-in customers usually prefer tax-inclusive pricing because it matches the price customers see; B2B-heavy businesses often prefer exclusive pricing so the tax is visible line by line. Pick one and apply it consistently — customers and staff both get confused when it changes bill to bill.
4. Get your invoice numbering right before you sell anything
GST invoices need a consistent, sequential numbering scheme per financial year — skipped or duplicate numbers are a red flag in any GST audit. Set your invoice prefix and starting number before your first real sale, not after. If you run multiple branches, each branch should have its own distinguishable series (a branch code in the prefix works well) so numbers never collide across locations.
5. Keep HSN/SAC codes attached to products, not memorised
HSN codes for goods and SAC codes for services are required on invoices above certain turnover thresholds, and they are also what your GST returns get summarised by. Attach the code to the product or category once, so it flows onto every invoice automatically — do not rely on whoever is billing at the counter to remember it.
6. Reconcile your GST summary before every filing, not during
Pull a rate-wise and HSN-wise summary of your sales for the period a few days before your filing deadline, not on the deadline itself. This gives you time to catch anything that looks off — a category taxed at the wrong rate, a return that was not settled correctly — while there is still time to fix it, instead of discovering it while your accountant is waiting.
None of this replaces advice from your own CA or accountant, especially for registration decisions and edge cases like inter-state supply or reverse charge. But getting these six things configured correctly from the start means your billing software is doing the routine work correctly by default, and the only decisions left for filing time are the ones that actually need a professional.