Book on sales as it relates to wholesaling?

Is there any books on sales anyone  enjoyed or thought was practical related to wholesaling? I am still getting my feet wet and currently working on my first deal. I am also continuing to work on estimating rehabs, finding comps and ARVs of property’s, but I would like to learn more about marketing and sales strategies as that’s the subject I’m the least knowledge on. 

I have read books on the process, but I am more interested if anyone has read anything more related to cold calling or talking to sellers as it relates to wholesaling that they think would be helpful for someone without any sales background. Thanks for the help!