Presuming you need to record all your transaction with every single detail, including your customer data, and you want to make the sell menu requires Customer Information, you can set it to default, so the transaction can not be made without customer information.
You can try this following method:
I. Set the default setting
Step 1, Go to Setup menu, click more setting, and select module
Step 2. Go to the Sell section and tick YES in Customer Required form, then Save
II. Sell Menu
After the save was made, you are not longer allowed to use Sell menu without inputting the Customer Information.