Eyelash Extensions... HELP!

Hey ladies! I have an opportunity to be a lash model for a local salon by my house, and the service is going to be totally free. I haven’t ever had eyelash extensions before but I love the concept. I’m a little nervous however, as I’ve read that some people’s eyelash were thinner and shorter after getting them done. My question is, is this something that would happen after one time (I don’t plan on getting them done again) or is it something that happens after getting them done over and over? I think it would be a fun experience and hey, it’s free, but if it’s going to totally damage my eyelashes forever it wouldn’t be worth it to me.