So who is your most important customer?
The one in front of you.
If they have signed a contract or purchased something over the counter from you, then they are very inclined to buy more from you right now. The add-on sales is easier than the initial sell to.
What do you have that you can sell that will go in line with your product that the customer bought?
If nothing is the answer think hard on what accessories or added features you can add since these will be very easy to sell to the customer and create additional income for you.
Also add-on sales can be as easy as mailing out to existing customers. The hitrate will be lower but the effort will be minimal for the cash earned. If you have big customers / few customers then going there with the purpose of add-on sales is not frowned up on but actually expected. In this way you will do a customer satisfaction meeting and having the opportunity to expand and deepen your cooperation with the customer and even develop new products for said customer.
If a customer wants you to add benefits /gadgets /change the product to better fit the needs of the customer should you do it?
Yes if you can treat it as add-on sales. In other words if the customer can pay for it or if you see a greater market potential in the suggestions.
So utilize old fashioned mail, email, the phone (or a telemarketing firm), book a meeting. Anything to get more add-on sales and think about starting a newsletter that will come out 1-2 times a year, chances are that the customer will appreciate it and create a mental note about it. and you can use this to launch new add-on´s for your products.
Add-on sales is good value for both you and your customers so take the opportunity to sell more!