If you think they’re just going to hand over some money so you can make the sale, that makes you anxious. Of course you won’t believe in what you have to sell.
But if you yourself see exactly how your product or service cuts their costs or increases their profits, then of course it makes sense and you believe in what you have to sell.
If you don’t already have enough knowledge of the product to sell it to someone else, do everything you need to get that knowledge.