$4,300 and six weeks on a building my lender was never going to finance

The percentage rule catches almost everyone once. What varies is the denominator. Some programs measure commercial area against gross building area, some against net rentable, and some look at what share of gross income comes from the commercial tenants. The same building can pass one test and fail another, which is why asking "do you do mixed-use" gets you a useless answer. Ask for the ratio, the denominator, and where it's written.

You got the earnest back and learned this for $4,300 on a deal you didn't close. That's a cheap version. The expensive version is closing with the 2.5 point lender because you're 12 days from losing $5,000 and telling yourself you'll refinance.

Honestly the thing I'd take from this is the order of operations. You did the property diligence first and the money diligence second, and the money is the part that's out of your control. I've been doing the same thing on the deals I look at and I hadn't noticed until I read this.

Five lenders in a market with real estate this size and only one workable answer is the real data point here. Small mixed-use is a thin financing market almost everywhere, and it gets thinner the smaller the building. Whatever you buy next, know who your three lenders are before you know what you're buying.

One correction to your own account. You wrote that the person you talked to didn't know the ratio rule existed. More likely he knew there was a rule and didn't know which bucket your building landed in, because on a loan officer's screen "mixed-use" is one checkbox and the overlay lives in a credit policy document he doesn't read. Same outcome for you. Different thing to ask for next time, which is the credit policy language, not the loan officer's memory.

$4,300 for a clean inspection report on a building you didn't buy isn't a total loss either. You know that block, you know what a barber and a tax preparer pay there, and if it comes back on the market in a year you're the fastest buyer in town.

I take about four months on decisions and threads like this are why. The question I'd add to your list: what does the lender need from the commercial tenants at underwriting? You found out at the end that the fifth lender wanted a year of operating statements from tenants who don't produce them. On small mixed-use the seller usually has a rent roll and deposits and nothing else, and if your lender wants tenant financials on a barber shop you have a problem that no amount of property diligence surfaces.