Initial Contact with Seller

I am very new at this (meaning I haven’t even done one deal yet). I have taken some training and have become pretty good at locating motivated sellers (my intention is to wholesale properties at first). I have found some potential deals that were listed with a realtor and some that are not. I can tell these were good deals because the dissappeared quickly!! I’m stuck on my initial contact with the seller. Any recommendations on how to make that first phone call to someone? If the house is listed, do I NEED to go through a realtor (either my own or the sellers)?