He has been doing flips for 30 years and claims to pay a great ROI and get equity in the flip as well.

Management fees, lease up costs, turnover costs vacancy rates, repairs, licenses,  non paying tenants etc. are all examples of these. 

There may be some instances where the buyer pays the commission to the real estate agent representing them.

I currently have 1 primary residence (still paying off my mortgage) and 2 long-term rental properties (both that I have mortgage on).

I’ve thought about selling our current house, using that equity to pay for a single family fixer upper that we’d work on for around a year, and do it again.

But you will want to evaluate it for yourself and see what you are actually comfortable paying. 

For example on SFR primary/second home properties, typically HELOC's are structured as a 30 year amortization, with the first 10 years usually being the 'draw' period (time to utilize and pay down the credit line) interest only and 20 years amortized principle and interest payments.

I'm not familiar with the Cuyahoga County tax site, so I could be misreading it.

The vision of this program is to help the investor determine if it is a viable file AND to monitor the property’s investment value after purchase.Deals are made based on two simple things:  Cost to the REI (cash out of pocket), and how someone/something else pays for the rest (terms). 

From a bookkeeping and tax perspective it is best to keep your personal and business accounts separate.