How can I increase sales through telemarketing? Is there any psychological/behavioral trick to make more sales?
Marketing is a must for selling. When telemarketing came, it was different from the conventional methods of marketing and proved more beneficial. Even today, telemarketing continues to be strong, and due to its direct approach, there is no replacement to it, in terms of sales growth. Based on my successful experience in telemarketing, I will tell you how to increase sales.

Obviously telemarketing is not as big as it used to be, due to new forms of marketing. But even today, where telemarketing can work, nothing else would work as well at convincing prospects, one at a time. Another advantage is that the cost of telemarketing is slightly lower than other ways of marketing, or a lot lower, depending on the comparison. There are a lot of strong points to telemarketing, and I will use those, in part, to answer your question.
There are several ways in which you can increase sales. However, I cannot rule out the possibility that you may be following them. Instead of repeating them here, I will focus on the most pivotal contributor to increasing sales. If you still want to know about the other ways, I would be pleased to discuss them, provided you let me know more about the products for which you do telemarketing so I have some context.
Even if you follow the latest techniques of increasing sales through telemarketing, if you ignore that special factor, then that could drain the sales. That factor is objections.
“That’ll take me too much time.”, “I am busy”, “Call me later” Hearing such lines over the phone is not uncommon for a telemarketer. You know that people on average are more ready to say “no” to buying something. As a salesperson, our job is to get sales, to find the path toward persuading someone into buying. Only a salesperson knows how difficult it is. That is the reason most salespeople switch into another field eventually. The one who gains mastery over the skill to analyze the customer behavior and then presents himself accordingly in front of a customer never feels a need to give up. Yes, analysis of customer behavior! That is what you seem to seek in the second part of your question, and mastering this concept will increase sales, even if you continue with your existing strategies. I consider that the chief contributor to increasing sales.
There are five most common, universal objections or doubts people could offer you when you would call them as a part of telemarketing activity (or in any marketing and sales engagement). Speaking out of my experience and the feedback from some top-notch telemarketers, if anyone works upon those objections from customers, sales could become easy. Each customer is different and has a different attitude, but those objections remain the same.
For that, you need not study behavioral or psychological topics. I have eased that for you or anyone who wants to increase sales, especially through telemarketing or door to door selling, in my post: 5 Deep-Seated Customer Doubts That Kill Your Sales (And How to Erase Them). As I have used visuals for a better explanation there in my post, so I would recommend you to read that by visiting the above link, as copy-pasting those points in this answer could make this unnecessarily lengthy.
Please feel free to reply to me in case you seek more information on any of the points discussed above, or in that post.
Good Luck!
Thanks,
Cleo