It internally calculates a rating for the weapon and looks up (the same)tiers/weapons with a similar(similar as in, there is a set margin it can look for below and above your weapons calculated rating to determine price) rating stored in the market (suffixes/traits get added to this rating as well) to determine the estimate price. The one that is 1k has a better chance, so I'm assuming your bellum also has a better chance that a 1 in 10.
If you have a really good version of the tier, a really bad version will not affect the estimated price.
If you have a really good version of the tier, a really bad version will not affect the estimated price.
x1