The answer is an entire blog post.  

Short Answer: 

Trust Estate: The Trust document or Certification of Trust

Probate with Will: Letters Testamentary (Full Authority) 

Probate without Will: Letters of Administration with Full Authority under IAEA. If Full Authority court approval is not required - unless there are objections

OR Limited Authority with or without bond. If limited authority court approval is required, it may be subject to the overbid process. 

A Certified Copy of the "Letters" is all I need. That is delivered to Title and Escrow, and the legal department does their thing and updates the Preliminary Title Report to the estate. 

I received calls from other agents in California asking me about this ... they did not check! This is why people need to know what the bleep they are doing before taking the listing! 

     Have your Title Company or Title Attorney run a search for you, or give you an opinion (preferably in writing via text or email).

   Many Title firms will do it complimentary if you are a "regular" with them.  Even if you have to pay a fee for the search, it's money well spent to save time and aggravation.

In Florida it would be the Letters of Authority issued by the court.

I never did in 15 years but I do know it's very different by state. I would never take someone's word for it, that's just asking for trouble. 

My first step in any listing is to do a search and hold with my Title Company.  I do not like surprises in the middle or end of any transaction.

This is a great question Steven Hoeke . On the few estate sales I worked they were usually trusted friends of mine who I knew well. In other cases they volunteered documents even without my asking.

We require full and complete copies of the trust or in many cases I speak with the family attorney or probate attorney. But, typically the trust confirms who the executor is or trustee(s) are. I also have my Title Company provide the Preliminary Title Report.

Steven, a good question thank you

Title insurance has to earn their keep & escrow has to roll up their sleeves & confirm it all Steven Hoeke 

You MUST. And yes the paperwork affirming who has the authority must be reviewed.

You have been asking some very interesting questions lately.  My answer to this one is that I typically do ALOT of work as  the deal progresses.  I work with the closing company daily to make sure all the documents are in place and if there are any surprises in line.  I hate surprises.  

We typically also have the will which is specific to what will happen with real property. (inherited or sold)

I take the seller's attorney's word for it

I haven't had to deal with such a thing, but I would definitely make sure any entity that has the final say will have their ducks in a row, haha.

I always refer to the title company with the documents I've been given and let them run them by their attorneys to see if they need anything else needed.

Oh gosh, it would have to come from an attorney to our attorney--I would be a fool to take the word of a seller! However, I've seen agents take the word of a seller because they have never participated in an estate sale/probate listing. It has created a whole lot of drama and an extended delay. 

We expect to schedule a meeting with the judge and get his permission to sell. Most wills allow the sale, but the judge has the final say.

Ask and listen to Kathleen Daniels, Probate & Trust Real Estate Svcs. 

They have documentation to prove their authority, and the title company will make sure that it is valid.