|There's some pretty good political scenes in Dragon Age|
Inquisition that you can use for inspiration.
As I wanted to build up to this encounter, Lady Darchana arranges for a meeting with them six days after they first enter Absalom and two days before the auction. Depending on the number of leading NPCs they win over to their cause, depends on the final price she will demand per person. Basically, the system is similar to Fame but the PCs can gain Fame for both winning over NPCs and other prestigious actions (namely public quests or performances). The starting off is 50gp per person (who may bring as many supplies as they can carry). The cost is reduced by 10gp for every 5 points they earn to a minimum of 10gp per person.
Goodmiss Alidane of House Candren who is the manager of Sea King Shipyard and member of the Docks Council will offer to use her connections to get them access to cheap but good quality food as she has recently met a sympathetic supplier - actually Doctor Rolth (resurrected by his allies in my game following the events of Curse of the Crimson Throne). The shipment is due to go out by sea vessel soon but if those passing through were to carry it, they could transport fresh food as well as dry.
Dirakah (actually a Gallu named Fennix who has an amulet that alters itself to look like a blue-haired gnome) is a merchant who has professed great interest in assisting Mendev's efforts, though he is keen to reinforce the fact that it is Mendev's problems. He has gathered a sizable donation (15,000gp) held within coffers that could be used to pay the mercenaries in Nerosyan. Naturally he doesn't mention that it is contaminated with Blood Veil (see Curse of the Crimson Throne AP). Fennix is a servant of Baphomet and holds great respect for the marilith general, Aponavicius, which only makes him more eager to hear of the PC's successes in taking Drezen.
Fennix is also in attendance though his plans are more long-term and he has nothing to do with the succubi's antics. In truth, it would slay them all if it knew for an attack at this auction would be far more likely to rouse the support of Absalom rather than cause them to shun Mendev as trouble magnets because Absalom pride means they can hardly stand idly by when this happens on their own land.
As Nocticula's servants are behind the sloppy strike, it is most assuredly to draw Absalom's ire in a roundabout manner though she would claim only a desire to capture the PCs. She will have recruited any succubi who survived the Sword of Valor's exploits as a secret partnership that would be alleged to please Baphomet - they would be aiming to slay the PCs, after all.