If all but three units are rented, the reason for the sale is not negative cash flow.

Example: most sales data for a house is public record and do you think you get the same value for a house with a mortgage as you do with clear deed?

You will want to dig much deeper than internet forums or even the sales reps at most self-directed firms to ensure you have a strategy that will produce results without unnecessary regulatory risk or too much administrative overhead.  

Do you see "moving sale" signs in the neighborhood? 

MMost agents are not business minded so you will need to find the ones doing the most sales as they will need more help and most likely are business minded.

In addition, you will need to collect sales tax/occupancy tax, if you do not and get caught, you'll be responsible for the tax. 

I specialize in homes going into foreclosure and short sales.

In New Jersey you cannot become a broker until you've been a full time sales agent for at least 3 years.  

I had a real estate broker license for about 30 years but I never did that full time.Always remember to do the math analysis on your prospects and try to look at them before you make an offer or at least have a clause in the sales contract that allows you the time (usually about 15 days) to make a detailed inspection of the subject property and possibly back out of the deal without a penalty that will excessively hurt you.There is so much to say to you but I am bound to forget something.  

You can judge how long it took them by looking at when they purchased the property vs. when it was listed for sale.