In such a scenario, an unsold should either be used to exclude sales as high outliers, or it should not be used at all; you don't cap sales that are unrelated to that BO at 23 - if the argument is that 23 is too high because it can't sell at that value, it should not be in the range itself. Exceptions to that can be made in a case where someone lists slightly lower than what they paid in items (e.g. if someone'd pay 25 in hats and instantly relist at 23, I'd be fine capping the sale at 23 as him relisting the new hat at 23 implies their buyout on the original hat).

This particular case is tricky for 2 reasons:

1) The low end is a buy order, but one that seems off as all other buyers are much lower, and his own buy order dropped significantly as well.

2) There are multiple sales above the seller, implying it does in fact manage to sell above 23 as well.

There are two solutions here:

1) You could give this a range of 20-25, where 20 has indicators its on the low side, and 25 has indicators of it being on the high side, effectively balancing each other out and placing the average right about where the current seller is at.

2) You could leave it outdated for now and wait to see what happens with the 23 seller.

Given the circumstances I would be okay exploring either options here.