When buying a house, should you follow the numbers exclusively?

[William Pope]

I have been looking at a 3-family house but when I run the numbers, the cash flow is in the red something like $230. Are there times when the numbers aren't showing the true value of a house? I asked him if he'd be willing to negotiate the price and he said he already had a full-price offer. I find this hard to believe. If he really did, why would he bother with me? I'm trying to find comps but having a time of it. House is in Passiac, NJ