Understanding the deposit that gets placed on your card.
Rental companies typically place a hold on your credit card covering the estimated cost plus a security deposit, which is released after the car is returned undamaged. This hold can sometimes take one to two weeks to fully clear even after return, depending on your bank.
Debit cards are often not accepted for this hold, or come with additional restrictions, so a credit card is usually the safer bet for a smooth pickup. Checking your available credit limit before a trip avoids an awkward surprise at the counter.