お客様のカメラは無料でお撮りしますって英語でなんて言うの？

Both of these answers are the same as saying "We'll take your photo for free with your camera".
To make it more formal, as you are talking to a customer you could also say "Excuse me sir/madame, but if I were to take a photo of you using your camera the photos are free."

"Also" is a way to show that they have another option, which is a free photo. "For free" is how you describe that a service or act does not have a cost.

I hope that this helps :)

If you do something 'for free' or 'gratis' then it means there is no charge or payment required.
"We'll take your photo free of charge."

"I can take a photo with your camera if you'd like."
Saying this will imply that it is free of charge by using their camera.
"I can use your camera for no charge."
I can use your camera is saying you'll use their camera. No charge means it is free.

One expression you can use is, "There is no charge for taking the photo with your camera."

No charge - no payment is required, you do not have to pay anything.

Taking the photo - Taking here is talking about the action of holding the phone or camera and pressing the button for the picture.

Camera - The word camera can be changed to
- Phone
- Tablet
- device, etc.

also suggests that there is more than one option so as well as paying for a photo you can 'also' take a photo of them with their camera
'for free' means to do something without it costly them any money

"We don't charge" - When this is said it means there is no price to pay.
Example - The restaurant does not charge people for water.