It's not really their job to do assessments, but the guards aren't busy so they're willing to take a casual assessment about the massive quantity of low-quality drops. Not counting Haroun's latest couple of drops, it's about 14 silver, they think. Haroun's drops from slime-fighting bring up the total to 31 silver. That's enough successful looting for Bella to get an E-rank tin guildplate once she gets back to town, and will net them 13 silver or so after tax.
One guard is writing down everything they brought out on a standard paper form. The other guard says she needs to take a look in Bella's and Haroun's packs, and pat them down using the Frisking Skill, to check for any extra loot they're trying to sneak out. Either of the two can ask for a guard of a different gender to perform the frisking, if they so prefer.