BO's arent meant to make outlier sales non-outliers. They're meant to bring sale values closest to their pure value as possible. The amount paid is actually relevant and can indicate whether or not a sale is logically conveying a common trading point. Sales far over a BO can mean multiple things: it can be an indication that the hats offered were overpriced, or it could have been convenience overpay (in the latter case, buyers on the hats offered often accumulate to a value close to the BO, meaning the alternative could have been to sell everything to buyers and simply pay the pure BO). It can also mean that we're dealing with a novice trader or one that otherwise makes very poor trade decisions. This last situation commonly happens with new hats and/or hats without buy orders, but is also really easy to spot if you see that same trader resell their hats far lower than they bought (and dumping in bulk where it'd amount for way less than he paid falls within that category).

Couple of examples where using the BO wouldnt lead to accurate values:

A recent example (which I think had your sale) was a hat where a sale was so far over the BO, that even at generic buyers, the sale would be higher than the buyout. The sale there was deemed an evident outlier.

Same goes for when you have sales at 68, 70, 72 and 500 (extreme example). 500 is clearly the outlier, and still is even if it had a BO of 80 and should therefore be capped at that, even though 80 is relatively close to the other sales. BO's shouldn't function to artificially bring sales closer together :P

This case falls in the last mentioned category; if we're going by BOs to attain a pure value we may as well also look at the barnstormer: with the BO there in mind and the adds that were given with it; even if we are given a BO of 80 on this sale, it means he paid 80 "pure" to then use it as ~35 "pure" in their next trade, thus basicly deleting half his currency in two trades