She took on the property management side for a reduced rate as I purchased the place recently through her.

How would most sellers react to a 3-4% interest rate?

I'm losing money $300 to $700 (with the last rent) each month on what was supposed to positive cash flow $176 a month on paper at 6.99% interest rate.

So my question is, how can I tell vacancy rates and if this would be a good deal? 

The US real estate economy in general has boomed thanks to COVID and previous rate drops.

Most mortgages are fixed rate.  

One of the properties has about 50K in equity built up with a low interest rate on a 30yr loan. 

My friend wanted to lend me the money for my investment property at the same interest rate as Guidance and I would pay him a fixed rate monthly and we would both own the property until I pay it off. 

So far, I paid below market rates because the building was severely under managed. 

Yes that can be an option but at the moment right now i have a deal in the works where i would need more then 50K to be able to make the numbers work I also recently went to a random bank and got a LOC for up to 50k at 11.5% interest rate with no fees.