Yeah, don't go cheap on things that can dramatically improve your income (working in sales or not). Books like this need to be re-read and marked, treated as workbooks.
Actually, I like Cialdini too, although he's not a salesman I think everyone should own a copy of Influence, for all sorts of reasons.
Tom Hopkins does a complete bible for sales, although somewhat boring.
I have a number of NLP based books such as Persuasion Engineering, but I wouldn't recommend it to you.
Some of the best, most engrossing reads are some of the oldies, you can probably get them from old book stores. Big League Salesmanship and Compelling Selling are the real deal.
Another book everyone should own, especially budding DJs is Get anyone to do anything, it's in the same vien as Cialdin's works and has useful research information.