I've seen this happen more than once. A deal lands on the table and the ARV looks beautiful. Purchase price works. Rehab works. Financing works. And once the property is renovated, the numbers say there should be a very nice profit waiting at the end.

Then somebody asks a dangerous question: "Where did that ARV come from?"

So we pull the comps. One sold for $620,000. Great. Except it’s half a mile away in a noticeably better neighborhood. Another sold for $635,000. Wonderful. Except it’s 400 square feet larger. Here’s one for $650,000. Perfect. Except somebody spent a fortune on the finishes, it has another bathroom, a better lot and a garage.

Suddenly our $625,000 ARV doesn't look quite so scientific anymore. That's essentially the problem in this deal: the projected ARV looked fantastic until the comparable sales turned out to come from a different neighborhood, with better finishes and larger properties.

And here's the uncomfortable part. I don't think most investors deliberately lie about their comps. I think we negotiate with them. We want the deal to work. So a quarter-mile becomes “basically the same neighborhood.” Three hundred extra square feet becomes “close enough.” A superior renovation becomes “we're going to make ours nice too.” A sale from six months ago becomes “still relevant.”

One adjustment at a time, every decision sounds reasonable. And somehow they all seem to go in the same direction. Toward the number we needed. That's when I get suspicious. Because Excel doesn't care. Put in a $625,000 ARV and it will calculate my profit perfectly. Put in $675,000 and it will calculate an even better profit with exactly the same mathematical confidence. Bad assumptions still produce perfect arithmetic.

But there's something else going on here that spreadsheets don't capture very well. Value depends partly on where you're standing. Imagine a property I have absolutely no intention of buying. It's too far away. Wrong neighborhood. Wrong kind of building. I don't need another project. I don't particularly like it. Now the seller tells me it's worth $600,000. Fine. To me, it may not be worth $600,000 at all. If you want me interested in something I don't want, it had better be a hell of a deal. Maybe at $500,000 I start listening. Maybe at $450,000 I get in the car. The further I am from wanting something, the more attractive the price has to become before I move toward it.

Now walk around to the other side of the table. I own the property. I've carried it for ten years. I've improved it. I've paid taxes on it. Maybe I raised my family there. Maybe this sale represents a big piece of my retirement. Suddenly every positive feature matters enormously. The renovated kitchen. The extra storage. The development coming nearby. The house three streets over that sold for $650,000. Of course I want the best price possible.

So where's reality? Somewhere between the buyer who needs a bargain before he even cares and the seller who can explain why his property deserves every last dollar. That's one reason comps matter. They're an attempt to drag both of us away from what we want the property to be worth and toward evidence of what other people have actually paid. But comps don't completely solve the problem, because somebody still has to choose them. And there is no perfectly comparable property.

Different street. Different size. Different condition. Different sale date. Different garage. Different view. Something is always different.

So judgment is unavoidable. The dangerous part is when judgment becomes advocacy. If I'm willing to use a larger, better-finished property because it's "close enough," would I also use a smaller, uglier sale from the same area? If every adjustment increases my ARV and none decreases it, I'm probably not estimating value anymore. I'm building a case.

Here's a test I like: "What comps would somebody use if their job were to prove me wrong?" Show me those too. Because the buyer has a number. The seller has a number. The investor trying to make the deal work has a number. The lender may have another. And eventually the market gets a vote.

Maybe that's why I shouldn't have one ARV in the first place. Give me the number I can reasonably defend. Give me the number if things go well. And give me the number if the market doesn't cooperate. Then show me whether the deal survives all three.

Because the dangerous question isn't: "Can I find a comp that supports $625,000?" With enough searching, I probably can. The dangerous question is: "If I didn't already need this property to be worth $625,000, would I still have chosen that comp?" That's where I suspect reality starts.