TLDR: AI can audit your vendor bills for $20 a month. One owner says ChatGPT found about $45K in billing problems over 3 years. This week's play: pick 1 vendor, upload 3 to 6 months of invoices plus your agreed pricing, check every flag yourself, then contact them.
The cheapest AI win I've seen this year is also the most boring one.
You hand it a stack of vendor invoices plus the price you agreed to. Then you ask it to find every spot where the two don't match.
Mitchell Hashimoto (the developer behind Ghostty) did exactly that. He says ChatGPT helped him find about $45K in billing problems over 3 years, on roughly $1,800 of ChatGPT spend. His words: it "paid for itself 25x."
So this week's play is the Invoice Double-Check. It takes 60 to 90 minutes the first time and about 15 minutes a month after that.
Why invoices are the safe place to start
Every service business pays bills that get approved on a glance. Fuel surcharges, linen services, software seats, the parts supplier, the uniform company.
One error at a time, it's small. A duplicate line. A fee you never agreed to. A price that crept up without anyone sending you an email. A delivery billed to the location you closed last spring.
But they stack. Month after month, vendor after vendor.
And this is about the lowest-risk way to put AI to work in your business. The AI points at problems. You check them. Then the vendor has to confirm every claim before a credit ever shows up on your account. Worst case, you spent an afternoon and learned your vendor bills clean (which is good news too).
The play: The Invoice Double-Check
Time: 60 to 90 minutes the first time. About 15 minutes a month after.
Tools: ChatGPT or Claude. A free tier works for a first test.
Step 1. Pick ONE vendor.
Choose one you pay often. Weekly deliveries, monthly service, subscriptions, anything with a lot of line items. Frequent bills give the AI more to compare.
Step 2. Pull 3 to 6 months of invoices.
PDFs are perfect. Then grab whatever shows the agreed pricing: the quote, the contract, the price sheet, even the email where they told you the rate.
Step 3. Upload both and give it this prompt.
I'm attaching invoices from [vendor] for [months] and the pricing we agreed to. Audit every line item against the agreed pricing. Flag:
- Charges above the agreed price
- Duplicate charges
- Fees that aren't in our agreement
- Charges billed to the wrong location or person
- Price increases I wasn't notified about
Give me a table with: invoice number, date, line item, amount charged, agreed amount, difference, and the exact evidence from both documents. If you aren't sure about something, say so. Don't guess.
That last line matters. You want it to admit when it can't tell.
Step 4. Check every flag yourself.
Put the invoice and the contract side by side and look at the line with your own eyes. AI misreads things sometimes, and you're the one whose name goes on the dispute.
Step 5. Have AI draft one polite email per vendor.
Paste in only the flags you confirmed and ask for a short, friendly note asking for a review and credit. Keep the tone "help me understand this," because you'll keep working with this vendor. You edit it. You hit send.
Step 6. Repeat monthly.
Once the first audit is done, each new month is one invoice and one prompt. Call it 15 minutes. Then add a second vendor when you're ready.
4 rules before you upload anything
Vendor bills, yes. Customer or patient data, usually no. If your invoices carry patient names (labs, medical suppliers), black those out first or skip that vendor.
AI never sends a dispute or pays a bill. It drafts. You decide.
Keep it out of tax and legal. If a flag turns into a contract fight, that's a call for your attorney or CPA.
Use a business plan if you have one, and turn training off in the settings so your documents aren't used to train the model.
Leverage Math
LEVERAGE MATH: What does an invoice audit pay back?
Case 1: Mitchell Hashimoto
Found: ~$45K over 3 years
ChatGPT spend: ~$1,800 over the same stretch
Return: "paid for itself 25x"
Hours spent: unknown
Case 2: Rebel Cheese (Texas)
AI tools: ~$200/month
Recovered: $1,500 to $4,000 per week in shipping overcharges
Payback on the monthly tool bill: about 1 day, even at the low end ($1,500 a week is roughly $214 a day)
Claude found the patterns "within an afternoon"
Worth knowing: Fortune reports the savings dipped after the carriers adjusted. Once you start checking, expect the leak to shrink over time.
Your turn (fill this in after your first audit)
Dollars found and confirmed: $______
Tool cost per month: $______
Hours you spent: ______
Days to break even = tool cost ÷ (dollars found ÷ 30) = ______
Tool costs
Claude Pro: $20/month, or $17/month billed annually [verified]
ChatGPT Plus: $20/month [verified]
Both have free tiers, which are fine for a first test.
Here's my honest read on that worksheet.
I can't promise you a number. Some of you will run this on a tidy vendor and find $0. That's a real result. You bought peace of mind for an hour and a $20 subscription, and you know which vendor to trust.
And some of you will find a fee that's been sitting on every invoice since 2024. Either way, you'll know, and knowing used to cost a bookkeeper's afternoon per vendor.
So the math to watch is small. If one confirmed $20 credit shows up, the tool paid for the month.
This week
Pick the vendor tonight. Run the prompt before Friday.
Then hit reply and tell me what you found, even if it's $0. I'm collecting real numbers from real owners for a follow-up issue.
Nate
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