I never sold a horse through W farms, I was just a potential buyer. As a buyer I can tell you the staff was helpful, communication was easy, the videos looked great and the horses shown to their best potential. From what I can see the cost to the seller was quite high for the service. For a lower end horse it may not be cost effective as most of the cost of the horse would go to the commission and the boarding. An upper end horse would get a better price because the horse is usually sold at a higher price and that would probably get you the price you are looking for after the commission fees. I have been horse shopping for 2 years in southern California ( it takes a while to find the right one) From the hundreds of ads I have browsed through I did not see W farms all that much. Maybe I was out of their target market, but if your selling a horse I would go to a sales barn that advertises on many websites to get your horse sold quickly, which will save you money in board. Sarah Lockman seems to market many dressage horses for clients and is very visible for potential buyers. She is near Chino Hills. I never sold a horse or bought a horse from her but I have communicated with Sarah and she responds quickly to inquiries and that is a plus.
If you know someone who can take a decent video you may want to sell your horse yourself. Facebook has many sites selling dressage horses, and some boards are only for horses in California, some west coast only and some are us horses only. Best of luck selling!