Listed Property vs. For Sale by Owner

[Terrence Redmond II]

What is the proper etiquette when a property is listed?  Is it ok to call the home owner instead of the real estate agent?  Does it matter either way?  How does one handle objections if the RE agent is in the ear of the owner when your price is lower than what the property is being marketed as?  It seems that if the RE agent is not educated on how investors operate, that going back and forth would be bad taste.  I'm operating out of Pittsburgh,PA and surrounding areas if that helps.   Thanks in advance for any and all insight.