You will find it very, very hard to come away with just the one "free" image. I have never come across a hard-sell done like this - it's not an obvious hard-sell, it's very insidious, and even if you know how to handle salesmen and think you're prepared for it, it takes you by surprise.
You will be left alone in a warm, dark, comfortable room and will see gorgeous pictures of your gorgeous family blown up to fill a whole wall. The soft, tasteful music will relax you, and the darkness will make the colours brighter, clearer and more attractive than they would be otherwise, so that you may well be more taken by the pictures than you think you will.
They will show you the three best images put together as one large picture, designed to make you think how much better the pictures look when you have more than one of them in one frame. This image will come up more than once during your viewing and each time you will find it more appealing.
Then someone will come in and go over them again with you, picking out the ones you really like - and you'll then be left to look at them again. Even if you don't chose the image of the three pictures together, this will still appear with all the others you choose.
You will be relaxed and happy at this point and no matter how tough you think you are, you will want more than one of the pictures. They will then offer you a discount on their price list if you pay for your pictures there and then, and will make a big thing about how much more they will cost if you place your order at a later date. It's so easy to get carried away at this point, even if you had agreed not to fall for the marketing ploys.
The staff will use language like "images" and "works of art", designed to make you think of something permanent and timeless, rather than just a snapshot which you would change every six months if it was in a plain frame. They will correct you if you refer to them as "photographs" or "pictures", and they will stress the value of having original pieces of art work in your home.
They will, at this point, be falling over themselves to be nice to you. They will offer you coffee, compliment you on how well your children behaved and how great their images look, pass comments on how lovely you look in the pictures as they "help" you choose the best ones to look at again, they will speak softly and politely, nothing will be too much trouble for them. This will all change once you have signed on the dotted line and they have your money.
I hope that you can be as hard-nosed in the face of beautiful images of your children as you think you can ... because I couldn't.