I am under contract to purchase a Quadplex.

Single family has more stabilized as there is not enough people who can afford homes.The purchaser is two very distinct types of groups who buy MF vs. single family and single family is bought to own and occupy, MF is bought to generate money.

They develop, they build, they finance, they property manage, they will have HAO, cleaning crew etc. etc. etc. so the subsidiary companies make money every step of the way.From investor perspective: The investor pay $15 K to reserve the right to purchase 25 multiplex over the year of next 5 years. 5 each year.

I believe that many will be able to purchase a townhome or condo, but not that dream home close to the city. 

To be successful as a real estate investor in any form - except maybe purchasing the Vanguard REIT index fund - an investor needs education, knowledge and understanding of real estate principles, real estate law, and real estate finance.  

And the only "client" reviews I've seen mention that their customer service is non responsive and difficult to get a hold of once you're purchased their services.

Hello,I purchased my first rental property last year and rented it out for 10 months.

You purchased six properties, and we have to assume, based on your post, that you purchased and renovated them for below a current market value. 

Can anyone recommend any sites, courses, videos, or books to purchase so I can prepare for the test?

Purchase price: $375,000 Cash invested: $30,000 This was a 2 unit that I purchased in 2016 for $375K.