Agent incentive fee for showing my rental property?

[Zigmunt Smigaj]

I'm not sure but it seems unethical for a management company to ask me if I want to authorize a "agent incentive"  in order to get my rental property rented.  This company is also a real estate office and they use their agents to show rental properties in addition to selling properties.  What I don't like is this fee ($150, or $300 double incentive) almost gives the perception that if I don't authorize a agent fee then my rental will go to the bottom of the list and never get shown.  Is this normal practice out there?