I don't think there is much wrong with your advert but sadly it may be a tough time to sell a horse. It might be worth maximizing your chances by tightening up a bit the wording of the advert and changing the photos.
Suggested wording (use paragraphs if possible to make it read easier):
"162hh, dark bay, rising 13 year old WB by X.
A lovely family horse, Berta has been with us for Y years and is sadly for sale due to family commitments.
Berta is a safe, enjoyable hack, alone or in company, 100% in traffic, snaffle mouthed at all times and easy to stop even in large, open spaces. Never been known to buck, rear or nap, she would be suitable for a competent novice. She does not have competition experience but has nice paces and can work in a basic outline, so might suit someone who would like to introduce her to low level dressage or showing. Good to clip, box and farrier (currently barefoot). She is straight forward to handle, good to catch, not mareish and enjoys being groomed and pampered.
A good, long term home is very important for this special horse."
You may want to add a sentence if she can pop a fence or, even better, has been round a clear round.
Photos: one really nice conformation shot. One hacking shot either right next to traffic or bombing around a big field. One schooling shot BUT make sure she is tracking up, in the current photos she looks quite short which may worry a potential buyer given her age.