For MLS comps i use proximity and frequency of listing/sale to adjust price.

I've noticed a steady increase in the frequency of unsolicited mailers I receive offering my buy my house ("why worry about repairs, we'll buy you house as is, all cash, quick close" etc., etc.).

Those guys can tell you exactly who the good contractors are and who the ones to avoid are, based on their volume of material purchased, frequency of purchase, and payment history.  

@Alina Trigub Well, the frequency of transactions, especially in the commercial sector, is what would make me have a 2nd job at least at first. 

Age and condition of the property, quality of tenants, and frequency of turnover all influence this cost.  

Buyer has been making very irregular payments (irregular in the frequency and amount). 

(also hedge funds make up a far smaller percentage of trades than you would think and you are confusing high frequency trading with hedge funds.

I'm sure it varies by balance size and frequency of transactions

All counties have their own rules and contact them to get the details like frequency, the time, and where they are held,Most counties have what is called a "redemption period" of time that the previous owner will have to pay the taxes that are owed. 

It also strikes me as odd due to the frequency of investors citing that they don't want to get hands on with their properties because they state their time would be better spent finding deals, but then they go on trips all the time.