Bargains use yesterday's region/faction stats to choose a set of 'interesting' items. Only materials for profession products are considered.
Only popular items are included (seen on most realms) and chosen among those are market intensive items (those constituting top 15% by posted value). For items chosen this way, 14-day price trend is found and projected today's worth is calculated (PMktPrice).
Table will then list items currently on AH that are much cheaper than they should be :)