Come to find out tenants were just delinquent but for the sale the seller was forgiving the delinquencies to boost the rent roll. 

Ultimately a much easier and cheaper solution, at least for now.

Do you have any tips or systems in place that have boosted your property's ROI?

(what's the ultimate goal with RE and investing for you and your family)3.

Start by reading the Ultimate Real Estate Investing Guide: https://www.biggerpockets.com/guides/ultimate-real-estate-investing-guide/introduction2.

I went through a refi last year with a traditional mortgage bank. had the same scenario, first appraisal came back super low, we argued the valuation and ultimately got nowhere. we decided to start over with a different lender, and got a 2nd appraisal exactly 16 days after the first one was dated, and the valuation was almost $80k more. sometimes starting over is all you can do. 

What if you could add $200 / month in NOI (a 30-100 bps boost in cap rate depending on the asset value) without raising base rent?

Cost segregation can help boost cash flow, create substantial tax savings, and increase the profitability of the warehouse operation by accelerating depreciation.A cost segregation study is a strategic tax planning tool that separates the assets that have a shorter useful life and can be depreciated over 5, 7 and 15 years from the residential rental property or nonresidential real property that are depreciated over 27.5 and 39 years, respectively.

But I think once you are buying 3rd you should be lower leverage or have done value adds to boost the rents so have safer margin/ratio.

Honestly, which would you say is the ultimate challenge you face as an STR owner today?