How to motivate my realtor to sell my houses?

[Josh Miller]

I own 4 different homes that are all sitting on the MLS and I would like to sell them by the end of the year. Locations are:

Newberry, SC (listed at $45.5)

Trinity, AL (listed at $87.5k)

Heber Springs, AR (listed at $105k)

Gilmer, TX (listed at $49.9k)

All homes are slightly below market value and I could just wait for the houses to sell but I'm motivated and want to help motivated my listing agents.   Currently all have standard broker contracts at 6%. 

Is it ethical and legal to offer my realtors a $1,000 bonus if they can sell by the end of the year (within say plus or minus 10% of listing price)?  I have a couple concerns with doing something like this, one of which is if the home doesn't sell will I end up with a really disgruntled agent come first of the year?    

Is it common to offer bonuses to realtors in slower markets, any comments or suggestions are greatly appreciated.  Thanks