The $1 transaction you see on your credit card statement is not a charge, just a temporary hold on funds. It is not debited into the Grays account and Grays cannot access this money.
This pre-authorisation feature enables companies to check if funds are available on the customer's credit or charge card and reserve the funds without debiting the cardholder's account. Pre-authorisation provides a level of assurance that a customer's card is valid, has sufficient funds and is not stolen.
This process is not unique to Grays and is commonly used by many companies including hotels, car rental companies and online retailers.