Sai may appear throughout the tower, but only after killing every monster on the floor. She will offer the player to trade their items for another and provide Zenny or other Equipment, however, the items may be cursed.

Sai will take your cursed items, as well. Providing the player with yet another way to rid themselves of them.

Item trade: Edit

"Up for a little swap a doodle do? How about something of yours for this!"
This trades whatever item is on the ground, with one piece of random equipment (?) within your inventory. It does not have to be of the same type. (ie. running boots are on the ground, you trade and lose your rapier for a cursed set of running boots, which then replace your sliding boots).

Zenny trade: Edit

"I'll give ya this bag of zenny for everything you got. Ev-er-ee-thing! What do you think?"
This takes your weapon, trinket, boots, and spell book, but not your consumable.

Upon making 20 trades, she will give you the Trader card the next time you talk to her in the lobby.

Using the Trader card will guarantee her appearing after you clear a floor, but you will be unable to visit the shops.