I agree with the above posters.
Ad should have a short but complete description of the horse, what the horse can do, any limitations, etc. Just because you are not paying by the word does not mean the ad should include that time Uncle Vinny who has never ridden before got on Dobbin and managed to get Dobbin to do these nine amazing things that no one else had done on Dobbin before.
Still conformation photos of all four sides. No artistic eye shots. No artistic cute kissable muzzle shots. Untacked horse on level ground conformation shots.
One short video that shows Dobbin doing general riding stuff that it is claimed Dobbin can do. Not highly edited. Walk/trot/canter both directions.
Additional videos should be available to show more detail of anything that Dobbin does. Dobbin at a horse show, Dobbin at the mounting block, Dobbin being caught in the pasture. All separate videos so that trainer who does not care if Dobbin is easily caught does not have to watch that video.
Videos should not have music. Videos should not have special affects.