The broker's pro forma said this deal was an 8.4% cap. The T12 said 6.8%.
The gap was $13,664 of NOI — broker NOI $71,767 vs. actual $58,103. Four lines did most of it: vacancy underwritten too low, no management fee, taxes held flat, and no reserves at all.
I built the spreadsheet I now run every 3+ unit deal through — it puts actuals and the pro forma side by side and flags any line that's more than 10% optimistic, then ends with a verdict and a max safe offer. On that deal it came back NO-GO at the $850,000 asking price, max safe offer $776,298.
Happy to share the free one-page Lite Checker if it's useful: https://grantology3.gumroad.com/l/sekzi — it does the same 90-second NOI / cap / DSCR check. The full workbook is here: https://grantology3.gumroad.com