There is one simple tool that you can use to double or even triple your sales. Using a checklist allows you to sell customers on potential services in order. It's a good idea to record everything that happens and note how far the sale gets each time.
What goes on your checklist depends on your type of business. Ask questions that help your salespeople to identify the potential problems your services or products can solve. For example: "Did you have problems with X in the past? Is it still causing you any problems?"
Over time, patterns will start to emerge. And as the patterns become more obvious, you'll realize what works and what doesn't.
For example, perhaps you'll find that only customers who have already spent $500 or more are receptive to upsells. Maybe customers are more receptive if you upsell them a smaller-ticket item first. Regardless of what you find, use the information to improve your checklists. It's like applying your website A/B testing to your sales process.