People all of the time, "over estimate" the opportunity and "underestimate" the cost and challenges in doing a profitable flip.

I could put a down payment for a conventional (20-25%) 550k duplex, but I feel it could hurt my chances of buying as many duplexes in a 5 year period (for example) if I go conventional VS an FHA at 3.5%. 

I was in your spot at 23, took a chance, and started a business.

Not a chance.  

Larger owners tend to analyze market rents monthly or even weekly and manage rents (or incentives) the best way they can.As long as the owner is engaged, the chance of adjusting rents is higher.

Class action lawsuits might still be a practical solution to the problem, but, if the statute of limitations is not waived, there is no chance of combining the original cases as their time to file has run out.

Ask them to do a cost estimate.

I pushed the deal forward with multiple banks understanding that there was a good chance a banker would get pushback from underwriting later in the process.

My partner called the owner who had give the original estimate, said no way are we paying until the job is done. 

This is true, but can increase your chances of success by working with an experienced team.Financing Challenges: Unexpected rate hikes or tightening lending restrictions can complicate your plans.