Limit items in cart?

[cpusa]

Hi,

 

Is there a way to limit the number of items in the cart? We sell 1 product at 4 different price levels. I want to make it so that there can be no more than 1 item in the cart at any time. If the user add's "Item 1" to the cart, and then goes back to the cart page and picks another one, there are then 2 items in the cart. I would rather that the cart be cleared out so that only 1 product is in the cart at any given time.

 

Upgrades would still be doable.

 

We're using WHMCS as a SAAS cart, so I hope this is possible. We just purchased WHMCS yesterday.

 

Thanks for your help!