We have larger photos available for you to purchase.
If you like this you may want to consider purchasing the larger version.
"We have larger photos available for you to purchase." This is a direct way to let them know that you have photos that can be purchased.
"If you like this" gets them to think about whether the item is something that is right for them before you mention it is available to purchase.
"We have larger photos available for you to purchase."（もっと大きな写真を買うこともできます）
これは、写真を買うこともできると単刀直入に伝えています。
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買うことができると伝える前に、"If you like this"（これが気に入ったなら）と言って、その商品が気に入るかどうか考えてもらっています。
If you want this photo in a larger size, please purchase one.
こうも言えますよ、
If you want this photo in a larger size, please purchase one.
(もしこの写真をもっと大きいサイズで欲しいのなら、購入してください)。
*purchase 購入
又は、
If you want this photo in a larger size, please feel free to purchase one.
(もしこの写真をもっと大きいサイズで欲しいのなら、気軽に購入してください)。
*feel free は 気軽に、という意味です。
*この言い方のほうが プレッシャーをかけず、フレンドリーな感じです。
値段をいうときは、
One large photo is 500 yen. (大きい写真一枚は 500円です)。
参考に！
If you would like a bigger picture, you can buy/purchase one
You can buy/purchase a bigger picture/photo if you would like to
Then you are talking about spending money to get something this is called to 'buy' or 'purchase'
You can use the terms 'photo', 'photograpgh' or 'picture' to explain what you are talking about
Large photos are available for purchase, if you are interested.
If you like the photo, you can also buy a larger version.
Larger versions are also for sale.
In common usage, purchase and buy are equal. However, both express that the photos are for sale and are not free. It is important to use one of these words to avoid confusion.
I would also use the word "larger" if I was trying to sell photos. It explains that it is the same photo, just bigger. This will help to tempt people if they want to display the photo.
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