Is there any difference in the frequency or extent of the problem within different types of property or based on their size or their floor plans or their geographic locations?

Clearly, the septic system is part of that.You'll get a large range of opinions regarding the frequency of required cleaning.  

I know that no matter what list or what frequency I mail I will need to be consistent.

You want a targeted segment with much more frequency (hit them ads more often).

Sure I run across these types of deals every now & again and I shoot them out to my buyers but not at a frequency where people could build an entire strategy off of that kind of stuff.

I have had issues with being blocked though so I recommend being careful how many emails you send per day, the message, and frequency. 

Many are skilled at dodging bill collectors, and hence the frequency of default judgments for landlords where tenants never show up.

I was wondering if some of you could share how you direct mail when it comes to how many a month, what frequency, etc.

As far as frequency goes that's an individual thing measured by your level of sophisticationa and knowledge. 

It depends on the type of piece (zip letters, personal letter, yellow letter, small postcard, large postcard), the frequency in which you mail, the message, the audience, and many other variables.