it can be done when there are more sales above a certain point, with a solid, well bumped unsold (if theres plenty of sales).

My problem with doing this as its being done here is that such sellers (highest sellers that - along with others - render the high sale an outlier) suddenly start determining the range. If the seller wasnt there, it wouldnt need to be capped and 17 would still be an outlier, so it wouldve been lower. If he was selling at 14 or 15 for a long time, its still clear that 17 is too high and that the range should be the same as when that seller would have been 13, but using it like this, it would make the high end 14 or 15. the range would vary between 11-15 and 11-12 (depending on what the seller is at) because of an outlier sale :P