Yes. If it is material to the seller's decision to take or leave the deal, and you represent the seller, it cannot be omitted. 

I hate buyer love letters - they can be disadvantageous to the buyer!
A few years back, I got TMI in a financial statement . . . they spoke of how long they had been looking, this was perfect for them, and their financial position was very strong. Seller said great, I love these guys, they found their perfect building, counter at full price and no concessions! 

My advice to anyone needing to show proof of funds . . . do NOT send your bank statement showing you have much more than you're offering. Get a bank letter on letterhead that you have sufficient funds to close this transaction at X price!

Yes... our MLS has suggested that we talk to our sellers about not accepting these "love" letters.

We have been told in our are not to write buyer letters for years now. LA does not want any liability.

If I find out anything about the buyer I forward it onto the seller. Loose lips sink ships as they say. I work for the seller.

Yes.  Regardless of how you came into the information, you owe your client a fiduciary responsibility.

Sometimes you come into that information through a love-letter, sometimes they've accidentally including you on a confidential email or text.  But no matter how you came about the information, you must share what you've learned.

Buyer letters are up to the seller &  the listing agent to accept or decline upfront. If you didn't advertise "no buyer letters" then they did nothing wrong.

Buyer letters are perfectly fine unless the seller or listing agent is a racist, prejudice, a sexist or religious zealot...but if they are not, then the letters have no danger attached. It's bigots that made the letters fall out of fashion, not the buyers info.

It would need to be disclosed if it is a material fact that could or would influence the buyer in regards to dealing with the transaction.

I do what is in best interest of seller if I'm listing agent. I ask sellers at time of listing if they want to read buyer letters. Almost all sellers say " No".

Material facts may need to be disclosed.

Depends on the info, will it help my seller in the negotiations?  or will it be a fair housing violation?

The comment of no buyer letters is because it is becoming a liability issue in many instances.  Let the strength of the offer speak for itself.

Buyer love letters are a minefield waiting to explode. The discussion must be held between the agent and seller about the potential problem which may arise from such an attempt from a buyer to make their offer more attractive.

Other information that is shared, whether on purpose or not, must be evaluated as to it pertinence and importance to the overall transaction.

obligated is an interesting word. Depends on what was revealed as in potential "harm" to the seller. If small talk, the on point agent handles this

Listing agent works for the seller(s) and anything that is pertinent to the property must be relayed. I encourage sellers to pay more attention to the 4-corners of the contract rather than emotional add-ons by buyers looking to sway them with love letters. Also, if their offer is not accepted, they can cry foul and they have!

If I have information I present it.  If I send a love letter I make it part of the contract so stupid agents who think it's their decision realize it is not.

The listing agent is supposed to divulge all information to their client

Yes, if they divulge information you need to tell the sellers. As for love letters, we don't write them any longer. If they're sent to me I will let my sellers know what is in them. 

You work for the seller. What you know you should disclose. Like Lyn Sims puts forth "loose lips sink ships"!

I have found "love" letters sometimes work and other times sellers are not interested in "sob" stories. Any info you come across should be disclosed to your client.

If it's a part of the offer, they can't legally NOT present it (at least out here).  I've seen a few "If you send a buyer letter your offer will not be presented" statements in the MLS, for which I've wanted to submit an offer just to bring those people up on Code of Ethics charges.  Yes, these are long-time agents who should know better.  Even California's AoR Legal team has scaled back their anti-buyer letter rhetoric of late.

Buyer letters still get buyers the houses.

And to your question, if the BA divulges something of importance or value to the seller, you should let them know.  That's part of your fiduciary duty to best represent your client and give them all the information they need to make an informed decision.

No, not always, depends on what is said by whom.

My responsibility as a Transaction Broker is to the Transaction itself. Limited Confidentiality and Honesty. 

Single Agency is different and should be based on the relevance to the client.

It is my obligation to a client to tell them everything I know/learn about the other side.

Without scrolling down and seeing others opinions I'd so NO! I believe in order. Tell your managing Broker 1st and he/she/you can talk to the LA's Broker. If you (managing Broker) are not satisfied with the LA's Broker then take it to the RE Commission.

Perhaps that may depend on what information is divulged. 

What matters to my sellers is the price and terms of the offer. 

If anything is said with the intention of "influencing" do we then vet the facts to determine the truth?   

I would imagine yes, but I suppose it would matter what we are talking about