I've been looking at ALOT of sale ads lately, not just for miniature horses but more for normal sized ones. A lot of people post the reasons why they are selling and I have never looked badly at that. I feel like alot of these people are only listing their personal reasons because they want the readers to see that there isn't anything wrong with the horses that they are selling (bite, rear, kick, etc) and that they wouldn't be selling the horse if it wasn't imperative that they do so.
Sometimes people build their horses up so highly as being the perfect horse, yet it makes you wonder if the horse was so perfect, why they are wanting to sell it. If I see that they have fallen on hard times, then they are most likely being forced to sell a decent animal. When I see ads that don't mention why the person is selling, then I often wonder if the people have more horses than they can take care of (meaning I may not get a healthy or trained horse), or if they are lying about some of the details (soundness/behavioral). I hardly ever see "Need to make room for new foals" when looking at normal sized horses, it's almost always miniature horse farms that list that in my experience.
I like ads that have pictures of the horse performing the tasks that the owners say they can do (riding, jumping, pulling a cart), and decent, up to date pictures of the horse where I can tell what they look like. I hate when you see a picture of a horse, and you think it's the one for sale, then you get to the bottom of the ad and find out that it's just for referrence.