accidentaly according amount button buyer buying cart click digi enters goods increase increases item junkie manually number page presses product purchase quantity remains return similar twice update web

When I click add to cart and then return to the web page and then click add to cart for a second purchase of the same item, the amount in the cart remains at 1?

According to Junkie, my Q was similar with digi goods.

'Quantity in our cart only increases when buyer MANUALLY enters the number and presses the update button. If buyer simply presses the ADD TO CART button twice, we don't increase the quantity .. so there is no chance of a buyer "accidentaly" buying 2 of your product.'