Myra buys craftable items from you at a set price. She has one trade Caravan Market in each Realm. With the exception of the Market in Giovanni's volcanic realm, each Market has 6 items or sets of items that it will purchase from you at any one given time. If you do not like any of these offers, you can discard an offer, and after a time has passed, another offer will taker its place. The offers tend to vary based upon your level and on what you have sold Myra in the past. For instance, if you have already sold Myra one apple, the next offer involving apples may require 2 apples or 3 apples.
You can gain a level in Myra's favor by selling goods to the caravan indicated on a daily basis. The higher the level, the more goods sold required to advance to the next level. Each level gives you rewards, in gold, and resources such as Hinges and Padlocks, or rare items that could otherwise only be acquired from exploration or from Glurb.