Thank you for your question. This is not legal advice. For legal advice ask an attorney.
I have a couple of points to make:
First, your Realtor is your agent. That means when someone talks to your Realtor, it is the same as talking to you (so far as legal notice goes).
Second, what was the communication between your Realtor and the buyer's agent? Speaking for me, BEFORE an offer is accepted I talk with the buyer's agent and find out why they like the property, when they plan to move, I will talk with their lender to see how solid they are financially.
Third, once the offer is accepted, I monitor the contingency period carefully. If I sense that the buyers are at all shaky, then I will step up my level of vigilance. Usually if the buyers have a weak agent I can sense the lack of content in the communication. Some agents are just order takers and have not been trained how to guide a buyer through a purchase, so if I sense that the agent is weak I will try to help them by meeting them for the inspection, try to ask them questions (with their agent presents) to help them understand what it taking place.
If I get the impression that things are not going well, and in most markets appraisals are a concern, as well as buyers qualifying for financing, I will have conversations with the buyer's agent such as " So, assuming that the appraisal goes okay is there any reason that your buyers would not want to proceed with the purchase?" to find out what they are thinking. It they say "well, they think that the master bedroom might be too small for their furniture" then I might suggest that we measure the room and the furniture to see, rather than just say "Oh, thanks, you'll let me know if it does not fit" or something like that.
The role of the agents to facilitate the purchase process, meaning (IMHO) if we can uncover reasons that they buyers are having second thoughts then we either develop some work-arounds to make them feel better about the purchase or begin looking for new buyers. For example, in older homes buyers can get concerned about things like the dishwasher, water heater, etc. and may be unaware of home warranties and how they work.
The bottom line is that if both agents are doing their jobs diligently a buyer backing out should not be a surprise in most cases.
One more note---if the buyer's agent is not on top of things, I also will talk with the buyer's lender and if I sense that there are potential problems with qualifying, when I will suggest that we send the "buyer notice to perform" prior to the expiration of the contingency period to let the buyers and their agent know that we are monitoring their progress,
Particularly with appraisals, I show up and meet the appraiser, will have any supporting data to help establish the value of the property. One sale I had in December I brought the file that included the building permits. If I had not provided the permit for the addition, the appraiser told me she was not going to count it.
Happy New Year!