There are eight merchants, each looking to buy five items. This matches with the forty items you can acquire from quests. The five items each set a merchant wants share a property, and each set can be ordered. Match each item with the number in that box for the merchant, then extract that letter from the item name. The extracted letters read SELL THIS USELESS JUNK AND GO ON A SHOPPING SPREE. When solvers submit this answer, they receive six new items in exchange for their current inventory.

Merchant	Items
Facetious Frank Frank’s items each contain a single vowel repeated five times, ordered by the vowel.	7 Madman’s Jackal Mask 8 Severe Beret 3 Lil’ String Bikini 5 Worn Loop of Gold 5 Burnt Sulfur Lugnut
Suitable Sarah Sarah’s items each display a different suit from a deck of cards (including joker), ordered by the number of items of the suit displayed.	1 Harlequin Doll 5 Cardiac Devices 5 Iron Shovels 11 Officer's Truncheons 1 Sparkling Necklace
Little Larry Larry’s items each include an SI prefix for a negative power of ten across the word break, ordered from 10-3 to 10-15.	10 Tamil Liqueur 3 Polyatomic Robot 3 Sienna Notebook 6 Mississippi Collectible 3 Unsafe Mtorolite
Star-Crossed Steve Steve’s items each have a hidden zodiac symbol in their picture and are ordered from Aquarius to Gemini.	9 Shield of Judgment 3 Neural Blade 1 Nebular Gloves 4 Tacky Jeweled Helm 5 Ultrasonic Boots
Holy Hannah Hannah’s items each contain one of the first five books of the Bible, ordered from Genesis to Deuteronomy.	7 Sega Genesis 13 Ultima III: Exodus 13 Leviticus Single 2 Lottery Numbers 1 Old Deuteronomy Sheet Music
Mourning Mike Mike’s items each contain a stage of grief, ordered from denial to acceptance.	3 Denial of Service Attack Plan 7 Anger Management Book 15 Bargaining Chips 18 Depression-Era Clothing 18 Acceptance Letter to MIT
Flag-Bearing Flo Flo’s items each have a semaphore letter in their graphic, ordered from A to E.	14 Architect’s Compass 3 Super-Accurate Tri-Square 2 Little Statue of Liberty 3 Fancy Pocketwatch 10 Broken Twig
Musical Maria Maria’s items each start and end with a solfège note, ordered from do to sol.	5 Domestic Avocado 4 Red Pinafore 10 Mint-Flavored Salami 4 Faded Sofa 6 Soldierly Parasol

Six Final Items

Wicked Cursed Broadsword -7

Wand of Vanishing +9

Holy Water of Blessing +7

Dictionary of Translating +3

Cursed Bunsen Burner -1

Calculator of Extrapolating +16