On any profile, you will see if you have used a chabber before. It is indicated by a small green mark in the upper left corner of the profile. That way, you can choose the same chabber repeatedly. See the example below. 

Through Chabber's chat system you can also text people you have previously hired and hear if they want to take a shift at your place again. In this way, you can encourage them to apply again. See example below.