I’m merely guessing, but it seems from many of your posts defending what the agent did, that you have gotten burned by a similar situation in the role as the seller in the past.
While I would never continue to show a horse that I had a deposit on for fear of the horse getting hurt, I can understand the mentality that says until the deal is done, signed, and paid for, I will continue to show the horse to potential buyers with the caveat to those potential buyers that I do have a deposit so if that falls through, I will contact you.
The agreement as OP gave us did not preclude the horse continuing to be shown as a back-up arrangement. Definitely lesson learned by me from this thread - if I ever purchase another horse I will be very clear with the seller about whether a deposit will remove the horse from the market until PPE/final payment/pick up or if the horse will continue to be shown to other buyers. Particularly in the case of continuing to show the horse - IMO there should not be such a thing as a non-refundable deposit - the whole point of non-refundable in my non-legalese interpretation is that if you don’t complete the sale as the buyer - the seller is partially compensated for the potential lost sales during the time the horse was not available to be seen.
We always tell shoppers on this site “until the horse is in your barn, it is not a done deal”. Definitely true in this scenario.
The issue is, and continues to be with this particular deal gone south is the agent being unavailable, not only continuing to show the horse to potential buyers, but actually putting up a new ad, and KEEPING the money as “a lesson” to OP. Crap happens - but in no way does this sound like a situation in which OP should be horseless and out north of $1K.