The id value (an 8 digit number) of the customer who has booked this. Note that for this application, you should assume that customers and CSRs know their customer ids. The system you are writing does not interact with these numbers, rather it simply records them. If this field is all blanks, the record is available for sale.
Does it mean that customer id MUST have all eight digits without leading zeros? OR at max. 8 digits and min. 1 (excluding zero)?
It seems sticking to all 8 digits is a better option. Please comment!