Would anyone mind sharing any free-to-use and reasonably reliable technique to estimate the rent of a rental property?

Many people seem to combine Dave Ramsey's technique with Robert Kiyosaki's- the author of Rich Dad, Poor Dad.

Any quick and dirty techniques during preliminary screening?

Second, you'd be surprised how accurate valuation techniques are sometime; usually they get you within +/-5% without ever seeing a sales contract.

So stick to where the people are moving to and living and that's usually the right technique.  

I use mostly direct mail campaigns, but am looking at branching out into video marketing, PPC marketing, and other types of lead and customer generation techniques. 

Use different techniques others are notusing.

page=1#p1868969 There are many creative techniques you can consider, I carry a pocket pack with me all the times to remind me of ways to do a deal.Some creative methods:Vertical break up (50% discount on properties)Hybrid offerDelayed settlementsJoint venturesFront porch offer, discount, nothing downMortgage out100% solutionsSubordinated  financingSeller participation Control and RollNothing down money backSplit notesCreation of paperPartners equityThese are a few of the many ways to close deals especially if it is a hard to close a commercial deal.My son, also an investor, always says, "Having many ways to close a deal is like a batter in a ball game who has 10 swings at a pitch instead of 3." 

How do I interpret this estimation technique?

Done right, a 30-year amortized loan can be paid off in 7 to 9 years using that technique, and the interest paid on it is much lower than if you took the whole 30 years to pay it off.David J Dachtera"Success is not a destination.