Keep in mind BBs is a frequency and reach marketing model.

Understanding REI, the velocity of money, leverage, and frequency of trade in a given area is one of the best ways to scale, grow, build cash flow, and create the ability to enter in those quality markets at scale as well.For example, if you had $30k and can only add another 20K to 30K at best per year for start-up capital, it would would take those 3 to 5 years to be able to possibly break into quality areas.

The bigger the deal, the higher frequency of custom contracts.

Of course this depends on how much money you make and the frequency of deals. 

I can't help you on the frequency with which sales are voided.

Did you notice a higher frequency of repairs from the tenants?

True service animals are different)As I get inquiries through Zillow, depending on the volume and frequency, I will just do an open house if I get a wave of applications initially.  

Hard money lenders are not likely able to do that because their terms are sort of in stone compared to private lenders lending out their own capital, which can be much more flexible in terms of rates, timeline, payment frequency, % borrowed etc.

Frequency with whichi you mail depends on the list.  

Quality, Quantity, and Frequency.