Perhaps there is seller distress and perhaps the other buyer had a unrelated issue that caused them to back out, but I would definitely want some answers to verify to be sure there isn't some underlying issue you aren't aware of.

Criminal activity is at our discretion depending on severity, number of convictions, and how long ago.We look for Income in sweet spot: rent 28%-31% of income, applicants who don't move every year (per credit report), applicants with bank accounts, non smokers, a verifiable stable source of income, landlord references, etc. 

It is not as immediate as a pre-qualification, as this process requires the collection of documents necessary to verify the financial health of a prospective buyer.

The main point that many investors try to make is to verify the numbers and information you are given regardless of who is selling it. 

It's a 4B3B SFH.After my purchased, I found out that some websites shows 3B3B while other shows 4B3B.Is there any proper way to verify these data?

If the credit report does not reflect the correct monthly payment, the lender may use the monthly payment that is on the student loan documentation (the most recent student loan statement) to qualify the borrower.If the credit report does not provide a monthly payment for the student loan, or if the credit report shows $0 as the monthly payment, the lender must determine the qualifying monthly payment using one of the options below.If the borrower is on an income-driven payment plan, the lender may obtain student loan documentation to verify the actual monthly payment is $0.

You may truly be in a market that's too expensive, but I would first verify if others are doing it in your market before completely writing it off.  

Are you able to physically verify there are people in the unit? 

Trust, but verify.

We always let them know the next deal we're trying to get as early as possible, and verify we can get more mortgages thru them - we haven't hit the "ceiling" yet.