An agent, or a REALTOR?
The Code Of Ethics outlines the latter.

Candice A. Donofrio nailed this one!

 Like Candice said Agent or a REALTOR

If a Realtor, the Code of Ethics from the National Association of Realtors (NAR) lays it all out

Candice A. Donofrio gave you a great answer. A

      None, unless I have a Brokerage relationship with them.  I cannot break the law or anything, but aside from that, I owe them nothing.

An agent has a different set of responsibilities than does a Realtor. A Realtor must always conduct his/her business following the Golden Rule - do unto others as you would have it done unto me.

All the fiduciary duties to a client. Not a client--I owe nothing but honesty.

My answer is the same as Lynnea Miller's.

It depends on the laws and regulations of the relevant jurisdiction, any association rules and any agreements between the parties.

Be honest and competent.

Honesty and integrity

I suggest you read the NAR Code of Ethics.

I second Candice. 

others have answered.

Read the Code of Ethics

To be a good egg!

To the client or customer with whom we have an established agency relationship:   As a fiduciary, we owe the highest standard of care:  Loyalty, competence, good faith, candor, obedience, confidentiality, and accounting.

To the those opposite the transaction table:  We owe a duty of honesty.

To fellow agents:  We owe a duty of good faith and fair dealing

To fellow Realtors:  (In addition to the duty to agents), The Golden Rule stated in the code's preamble is a broad statement of our responsibility, though the code embodies many particulars. 

To treat everyone fairly and with respect.  To do the best job they can and ask for help when needed.

To follow the Code of Ethics

Treating everyone fairly and honestly.

If you are referring to a REALTOR®, the National Association of Realtors has a Code Of Ethics.   In addition, each state has their laws for licensees to adhere to.  

Not all agents are REALTORS®, but I am one. I abide by the Code of Ethics which spells everything out pretty well. 

Oakly Rogers If a member of the NAR, abide by the NAR COE's. This sufficiently covers the agent's responsibilities to the public, customers and other real estate professionals. If not a member it is a good business practice to also follow these guidelines.

Honesty covers it broad based. From there it is dependent upon the realationship formed!

Treat them honestly and disclose material facts.

to do the right thing

Realtors have a Code of Ethics....follow them...all of them....

Follow the rules in your state.