Universal waiting list for examinees
Make a waiting list that all examinees can sign up for, and all VECs & their VEs can view & invite examinees to join their respective sessions. Examinees should be able to set bids of maximum fee they're willing to pay, that blocks any VECs & their VEs from inviting them to take an exam that costs in excess of their max fee bid (also, field validation to prevent inputs higher than the most expensive exam fee of any VEC so there's no appearance of bribery).
And possibly other examinee-limited variables that VECs & VEs would want to know in advance from potential examinees, such as "we don't want to test felons, are you?" or "we will make extra time for you if you're confident you will pass the next higher level exam(s), are you? click [tech] [general] [extra] for all the tests you're confident you will pass in a single setting".