Is there any way to enforce a minimum quantity to be purchased for selected items.
Yes, there’s an option in WSM under Settings → All Config Options called ‘Set Minimum Purchase Quantity’ that allows it. To make it work you have to create an integer type attribute in PAM that you populate with the minimum quantities for items that are supposed to be restricted (e.g. type in 6 if 6 is the minimum amount of that item that can be purchased), map it to one of your customnumber or customtext fields and point the WSM option to that field.
Here’s a KB article that explains it in more detail: Please Sign In - WebSell Portal
Can you do the same for Maximum Quantity?
Yes, there is a separate option called ‘Set Maximum Purchase Quantity’. You’ll find it in WSM under Settings → All Config Options.