Depends totally on what level of horse I am looking at and how the horse is described/why they are selling etc.
A photograph is a snapshot in time. The rider may be making mistakes but perhaps that means the horse will go a lot better when ridden correctly? Or perhaps if there is a problem with the horse then that maybe the reason why.
It is the horse you should be assessing - not the rider
It depends how the horse reacts to those mistakes...and how 'bad' they are, how long the rider has been riding the horse (if info provided) etc.
It amazing what lots of horses can tolerate and still work reasonably well.
However, I also cannot understand why people use completely unsuitable pictures in their ads