My worst (or maybe just the most frustrating to date) is hiring a Lumber Liquidators contractor to install my LVP flooring and making assumptions about quality of install.

Writing in loan assumption rights for a buyer can be huge as well when you sell when rates have gone up in the market in future years.Remember lenders say nothing is negotiable but really that is untrue.

It allows me to better question his assumptions and get more narrowly into determining what the end result will be. 

In addition to that, if the "assumptions" are realistic.

I have no knowledge of how that works.Vacancy (10%)Repairs & Maintenance (5%)CapEx (6%)Management Fees (0%)- I’ll be learning from this property, but hope to handle management alone.Future Assumptions: Ultra ConservativeAnnual Income Growth: 1%Annual PV Growth: 1%Annual Expense Growth: 1%This results in $573 in net cash flow per month, which sounds good.

@Kevin Phu 1k is exactly what my assumption has been when doing my analysis, but unfortunately, that wont be enough cash-flow for this deal to work out.

Even when going this route, your assumption is correct it will often times be based of comps since it is not a true commercial unit. 

I am of course starting at the seller's numbers but never really stay on those for too long... too much optimism baked in... but alas, such is the game we play.For POH's, what sort of expense ratio should be a reasonable estimate for modeling out realistic assumptions? 

I believe an assumption would require you to be an owner occupant.

I am outlining this under the assumption that the owner is unaware of the problem, as the tenant is dealing directly with the management company, and the management company is telling the owner everything is "fine and dandy."