The 24-hour hotel cancellation policy is pretty standard, so its should be little surprise that Booking.com charges a penalty for last-minute cancellations.
But there's an interesting question in here: Can Booking.com still charge those fees, especially if a credit card wasn't used to hold the booking? Fortunately, the golden rule applies, and it's only when there's a credit card on file, can they really go after you.
So if you didn't enter one, you're fine. Don't expect them to follow through on the penalties. (It seems like its there to mostly encourage travelers to cancel ahead of time to prevent hotels from losing money.) On three separate occasions in Georgia, I didn't cancel a stay ahead in time to prevent “paying a penalty.
The costs ranged from 0 GEL to 70 GEL, but Booking.com did little to claim the money. It's been several weeks since, so I assume it's all been swept under the rug.
For other questions, the Booking.com FAQ covers it pretty well:
Can I cancel or change my reservation through Booking.com?
Yes, it’s easy. You can cancel or change your booking by signing in to your account. If you don't have an account, you can create one here. Please remember to check the property's cancellation policy before making any changes to your booking. Non-refundable rooms and other special deals can have a different cancellation policy. Room-specific cancellation information is included next to the room type under the "Conditions" column.
Does the hotel need a deposit or payment in advance?
Most hotels don't require a payment or deposit in advance. If they do, you can find the details under "Hotel Policies" on the hotel’s page and in your confirmation email.
Really, the only other price for not canceling in time is a conscience.