Add-ons can be manipulated via the Dev Console

[Valentina R]

Let’s say a site uses the select dropdown add-ons with extra prices. If you delete every single choice except the one you need and click add-to-cart, it will add the add-on value without adding the extra price it comes with.

There should be a check for the price when clicking add-to-cart of some sort that would add the price from added add-ons - if not already done.

A client here has had this happen in his store.