To be clear, a recession could occur, home prices could fall, cap rates could increase (and multi-family prices fall), banks could tighten lending standards, etc, but right now, market participants are making rational decisions based on the information they have and cash flow can service debt without relying on rent appreciation. 

If your numbers are tight to begin with, anything going wrong at any stage -- purchase, rehab, renting, refinancing -- can put a strain on the deal.Don't do the deal if you don't have reserves and can cover holding costs.Expect 8 months of holding costs because typically you can't refinance until 180 days post-close, and then it takes maybe a month or so to actually refinance from there start to finish.If you can't BRRRR comfortably (e.g. leaving money in the deal or not cashing out) then it may not be a good idea until you're ready.Most lenders will be around 70% LTV, not 75%.

David, Are you starting to find that banks are beginning to tighten up on letting investors pull money back out of properties?

If Trump is reelected, those relationships will only be further strained.

@Yuhei Kato you're probably not going to like my answer but if you already own one home and don't have the money for a down payment you need to tighten up your finances and save one up

I have run the numbers and it will cash flow really well, but my question is wouldn't that put a tremendous strain on me only owning half of the duplex. 

Matt (above) and myself also flip properties, the margins have to be a bit bigger to deal with the licensing side of things and as the market has been rising cities have tightened their belts a little bit on contractors and investors.When I got started in 2007 I did everything wrong, the cities knew it but they were just happy that we were fixing some of the dumps and never mentioned it to me. 

The risk substantially increased given that we are approaching the end of the US business cycle and most importantly when China began reducing foreign capital outflows of their citizens into assets, especially Real Estate really began to tighten in late 2018.

At what point does the market tighten so much that the local "deal" isn't even that much of a deal anymore?

Your RE investments should not put a strain on your personal money, and vice versa.Other than that, which you may have already taken care of, I wish you the best!