To prevent the users from having the ability to choose the Place Order button, you can remove the permission IBE_CREATE_ORDER from the role(s) in the CRM HTML Administrator: Settings tab, Security ->Roles and search iStore role(s), remove this permission.
An option is to then use request sales assistance. The iStore role(s) would need the IBE_ASK_SALES_ASSISTANCE permission to be able to request
sales assistance. For more information on this permission, see
Implementing Customer Assistance, page 14-1 -