I recently purchased my first property which happened to be a commercial property that has, among other things, a 2 bay automotive repair shop/inspection station.

In that case you'll need to ask the seller to replace at his cost followed by an inspection that you will pay for.

You can invest in class D areas that on paper will show a high IRR of 20% but I would not touch it with a ten foot pole, but in same breath I would consider a 10% IRR where there is no leverage and low investment to value.If the class(a,b,c,) of an apartment building is based on the year it was built than what specifically determines the class of the area?

@Dale Linenot in a million years.the whole point of investing in RE is to build equity over time.  

For myself slowly building an REI portfolio has worked best. 

Free attorneys from tenant-support groups are very effective in finding ways to block and delay.PS: for anyone interested in supporting our landlord legislative efforts please join the Rental Property Association of Wisconsin RPAWI.org which is a Milwaukee-based non-profit.Cashflow in Milwaukee is still possible at current interest rates, but you have to be careful to not "buy cashflow" with a huge capex liability that comes with old buildings! 

All great advice but most important build your network around you.

If anyone plans on doing short term rentals to some degree or building additional living space, then this is imperative. 

Some buy and hold investors may have outdated beat up buildings that can't be sold conventionally without repair and your flipping operation with the right agent may just happen upon that deal for working with that person.

The house is build in 1875.