Depending on the color and combination of the armor and weapons you're wearing, the save crystal shopkeeper will give you a rating based on your appearance. If you can get a high enough rating for both characters, he'll give you a special item. The following is a small list of some of the highest rated items by the shopkeeper's standards.

SHARLINE:

Avenger

Armor Of Frost/BLUE
Flayed Skin Armor/RED
HRL-OOO-A/RED
Paldio Breastplate/BROWN

Dragolos Boots/BLUE or BLACK
HRL-OOO-B/RED
Speed Boots/RED

Billiana Hood/YELLOW
Divine Halo/YELLOW
HRL-OOO-H/RED
Pot/YELLOW
Rabbit Helm/RED

Band Of Clarity

DARIUS

Bloodclaw

Absorption Armor/BLACK
Darkforge Armor/RED
Flayed Skin Armor/RED
Volt Suit/YELLOW

Armored Boots/RED or SILVER
Speed Boots/BLUE
Woven Boots/RED

Azure Headband/BLACK
Divine Halo/YELLOW
Jemila Ribbon/RED
Paldio Helm/RED
Swan Beret/BLUE

Elder's Ring

Note: Also, keep in mind that you will get better ratings if what you're wearing matches or if it's all the same color. It's also better if your equipment is at max upgrade level. For example, if you wear all the HRL gear colored RED for Sharline, you'll get a perfect rating from the shopkeeper.