If you are going to sell then you must understand the tax implications. 

This is a self directed RRSP or TFSA account that allows you to lend your money out to people with the backing of their mortgage for a high interest rate. 1st, 2nd, 3rd mortgages, down payments, refinances, flipping or renovation money.

Is this expected since interest rates are high and listing prices are subsequently dropping? 

Typically its done for open space or use for community property (ie. fire station location or other county use) and typicaly would assist in increasing tax base.  

Knows real estate tax write-offs and how I can best apply them!

If you aren't familiar with Baltimore, I would suggest it's a hard no and say that you are trying too hard to make cash flow happen talking Baltimore and tax liens and auctions.

I recommend that you look at Notice of Defaults, Vacants, Tax Liens or Probate. 

Whether you need a CPA with just three rentals depends on the complexity of your situation and your comfort level with DIY tax prep.If things are pretty straightforward, you might be fine with tax software for now.

There may be something called a "Due On Sale" clause.Check and see if all tax parcels are included in one mortgage or if they have separate mortgages.You have to have him spell out what he considers to be a "partial seller financing".

Fort Collins did it since the 1960s and only recently created a law against it because of rent rates.