How are you refering them? What is the type of media in which you are marketing?
If you are on the internet (I am no guru) but I am sure there is something that you can have on your website or program that will tell you how many clicks are going to their site.
If you are a face-to-face type refferal, get to know the client and have them contact you after they have completed the process. This way they can let you know how the service was, and if they recieved such items for a gift. Then you have a background on what is happening.