Specifically, do you look at comps on the market or try to find what value would be based on the cap rate? 

I clicked on the link and their starting interest rate is 11.1%.

Every time I inquired about commercial loans on my SFR I got quoted much higher rates and loans that were amortized over 30 years but always callable every 5-10 years.

Drop your thoughts below.

If the loan amount exceeds $1M, then rates are in the high 6's to mid 7's. 

I believe there are high interest bearing amounts that are similar to CD rates but they give you the flexibility of having all the funds available to you immediately.

I also have a primary residence with nearly a JUMBO loan at a high interest rate and I own a vacation place in cash (small trailer not worth much money but i also own the land) in a different state that I pay RE taxes on. 

I don't think I would advise anyone do something or not do something because it might be a "red flag" - yes the IRS has plenty of red flags, but the audit rate on most of these issues is so comically low, that as long as you have a legitimate position - take it, don't not do it just because it might slightly increase your chances of an audit. 

Then your monthly need drops (less mortgages, kids grown) and you realize you stayed in a bit longer than you had to but it wasn't all your fault because you wanted to (and did) tap out at the top in Q2 of '22. 

The duplex was expensive and with rates as high as they are, I was not able to save money house hacking.