Why double allocation keeps happening, and what actually stops it

Every developer who has sold more than a hundred units has a version of this story. Two agents, one unit, both convinced they sold it. Two receipts. Two customers who have each told their family which flat is theirs.

The instinct is to blame the agent, or the spreadsheet, or the fact that somebody did not refresh a shared file. None of those is the cause.

The actual cause

Two people can hold two different truths about one unit at the same time.

An agent works from a copy. The office works from the master. Between the moment a reservation is agreed on site and the moment somebody types it into the master file, the unit is simultaneously available and sold, depending on who you ask. The gap might be twenty minutes or three days, and the whole risk lives inside it.

Everything else is a symptom. A shared spreadsheet does not fix it, because a shared spreadsheet still has that gap — it just makes it shorter.

What it costs

More than the refund. A double allocation costs:

• The refund itself, usually with a goodwill top-up
• The relationship with whichever customer loses
• The agent's confidence in the inventory, which means every future sale gets slower because they ring the office to check
• Whatever that customer tells the next ten people who ask about your estate

The last one is the expensive one, and it never appears in any account.

What stops it

The unit has to hold its own status, and that status has to be the only one that exists.

• Reserved means reserved for everyone, immediately. Not after the sync. Not after the office types it in.
• The reservation is made against the unit, not recorded next to it. If two agents try, the second attempt is refused rather than accepted and reconciled later.
• A reservation expires on its own. Most double allocations start as an old reservation nobody released, so an agent treats a stale hold as fair game.

The test of an inventory system is not whether it can record a sale. It is whether it can refuse one.

What software does not fix

If your sales process genuinely allows a unit to be promised verbally before anything is recorded, no system will save you. The software can make the recording instant and unavoidable, but somebody still has to do it before they shake hands.

That is a management decision, not a software feature — and any vendor telling you otherwise has not implemented in a real sales office.