That's called cart abandonment. This might be due to many reasons like 1. additional charges while checking out 2. long signup forms 3. Slow loading speed or some site bug. Get you site tested properly, check the page speed and loading time and get a better server if needed. If signup form is lengthy, add social login to it, this will help user signing up within a click. Loginradius, gigya and janrain are the top social login providers currently. I would recommend Loginradius for its best prices, support and having b2b audience as target.

First is to check the process of how your visitor experience your site. Is it friendly? Does the pages load faster? Shipping fee cost (as what is mentioned above)?

Then you ought to check if how long does an average visitor stay on the pages of your site. How are they behaving?

Next is the copy/content of each of your pages - do they convey well the message you wanted to convey?

Do split testing and figure out which layout/content/design best works for your target market.

For me, I abandon my order once I see how much the shipping cost is. Sometimes there's an error in the site, or the page is taking too low to load. I might not like the payment method too.