Match the invoice to a purchase order or work order
Every vendor invoice should trace back to a document your team created before the work happened — a purchase order for materials, a work order for labor. Pull that document and compare four fields: vendor name, property, date, and scope of work. An invoice with no originating document is billing for work nobody authorized. Occasionally that is fraud; far more often it is a standing arrangement no one has reviewed in years, which drifts just as expensively. The red flag at this stage is the rounded lump sum — a single figure labeled "plumbing repairs" where line items should be. A legitimate vendor can itemize parts and labor. A lump sum cannot be audited at all, and vendors know it. Ask for the itemized version before approving payment. The request alone tends to improve the next invoice.
Verify quantities against what was actually delivered
An invoice states what you were billed for; a packing slip or delivery receipt states what arrived. Compare them line by line, and have the maintenance tech who received the order confirm the count when the paperwork is missing. Watch the unit of measure — the classic quantity error is a case-versus-each mismatch, where the order was twelve units and the bill is twelve cases. For services, check billed frequency against the site log: a weekly landscaping invoice should match the weeks the crew actually appeared. The red flag here is quantities that match the purchase order exactly on every invoice, month after month. Real jobs change midstream — parts get returned, scopes shrink. A vendor whose billed quantities never deviate from the PO is billing from the PO, not from the work.
Check every unit price against at least one other source
This is the check most operations skip, and it is where the money is. For each line item on a vendor invoice, compare the unit price against at least one independent source: the supplier's published price, a second distributor's price for the identical SKU, or your own history — what you paid for the same item last quarter, and what your other properties pay today. The comparison must be at the exact SKU level; a "similar" part is not a comparison. The red flag is the same SKU priced differently across properties in the same portfolio. That pattern means the vendor prices by relationship, not by contract, and each property is negotiating alone. A structured supplier price comparison makes this check repeatable instead of heroic, but even one alternate price per line catches the worst of it.
Add up the math, including tax and freight
Arithmetic errors survive because nobody expects them. Verify three layers: each extended price equals quantity times unit price, the line items sum to the subtotal, and tax is applied at the correct rate to taxable items only — in many states labor is not taxable, and a vendor who taxes the whole invoice is overcharging on every job. Then read the freight line. The red flag is freight charged on will-call orders: if your technician picked the order up at the counter, there is no delivery to bill. The charge persists because it is small enough to clear approval without a glance. Finally, check the invoice number against recent payables. Duplicate submissions of the same invoice, weeks apart, are a mechanical error that recurs wherever approval and payment are handled by different people.
Look for the patterns that indicate price drift
Most vendor overcharges in property management are not single dramatic errors. They are drift: a unit price that climbs a few percent each quarter with no contract escalation behind it, invisible on any one invoice and obvious across four. The fifth check therefore runs across invoices, not within one. Pull a year of invoices for your highest-spend vendors and track the unit price of the SKUs you buy repeatedly. A price that rises quarter over quarter without an announced increase is drift. So is a lump-sum line appearing where itemization used to be, or a freight charge that starts showing up on orders that never carried one. None of this is visible in the week an invoice arrives. This is the check that turns invoice auditing from clerical review into expense control.
Manual auditing breaks at portfolio scale
The five checks work on any single invoice. The constraint is volume. NAA's 2024 Income/Expense IQ data puts multifamily repairs and maintenance near $1,098 per unit per year — on a 200-unit property, roughly $220,000 spread across hundreds of invoices and thousands of line items, and maintenance cost per unit keeps rising. The match and math checks fit inside weekly payables. SKU-level price verification does not. It is the first task dropped when the AP desk gets busy, and it is the one that finds the money. Systematic review means every invoice, every line, priced against verified suppliers, repeated quarterly so drift has nowhere to hide. That cadence is what The Benchmark runs as a product: the average annual savings it uncovers for a 200-unit property is $22,546, a 4.51x average return on the investment.
