Why IMEI-level stock beats a quantity count
Tracking each handset as its own record changes what you can see, sell and trust on the shelf — and it is the only way per-item margin VAT ever adds up.
A box of screen protectors is a number. You have eleven, you sell one, you have ten. Nothing about the eleventh is different from the third.
A second-hand handset is not a number. It has a cost, a condition, a battery health, and a history — and the one at the back of the drawer cost you £40 more than the one at the front.
Counting both the same way is where the trouble starts.
What "iPhone 13 ×4" cannot tell you
Say the shelf shows four of the same model. You bought them over six weeks: one trade-in at £150, two from a supplier at £205 each, one from a walk-in at £180.
The count says 4. It is even correct. But it cannot answer:
- Which one did we just sell?
- What did that one cost us, so what did we actually make?
- Which of these came in on a VAT invoice and which did not?
- Which is the one with the swollen battery the customer brought back?
Each of those questions has a real answer. The count has thrown all of them away, and the only place they still exist is in somebody's memory.
The moment it stops being an inventory problem
Most shops can live with a fuzzy count. What they cannot live with is a fuzzy margin.
The VAT margin scheme is a per-item scheme: the VAT you owe on a used handset depends on what that specific handset cost you, not on an average. Four handsets bought at four different prices are four different margins and four different VAT figures, and the record-keeping rules ask for a stockbook that tracks each item sold under the scheme individually (official guidance).
A line reading "iPhone 13 ×4" cannot produce any of that. Which means the choice between a quantity count and unit-level records is not really an inventory preference — it decides whether your VAT return is built on records or on recollection. There is more on the arithmetic in getting the VAT margin scheme right on used devices, and you can put figures through the margin calculator.
What a unit-level record actually holds
One physical handset, one record, carrying:
- An identifier — an IMEI, a serial number, or your own shop reference
- What you paid for it, and what you are asking
- Storage, colour, condition, battery health
- Where it came from
- What happened to it: received, reserved, sold, returned
The count then stops being something anyone types. Available stock is however many unit records are still available, which means it cannot drift away from the shelf — there is no separate number to fall out of step.
"That sounds like more work"
It is one extra field when a handset arrives. That is the honest cost.
What it removes is the work you are already doing and not counting: reconciling a count that drifted, reconstructing what something cost at quarter end, arguing about which handset the customer actually bought, and discovering in April that the margin you have been quoting yourself all year was an average of four different purchase prices.
You are already tracking these devices individually. The IMEI is written on the box, or in a notebook, or in a WhatsApp message to your supplier. Unit-level stock just puts it where the money is.
A note on identifiers
It does not have to be a full IMEI. A serial number, the last few digits, or an internal shop reference all work as long as one record means one physical device, and no two records share a reference. Perfect data entry is not the condition — one-to-one is.
Practical detail on how this works in SlickCell Pro is on the inventory and device units page.