Found this iPhone 15 pro max battery 86% , back is changed + there’s small yellowish dot in the display

He is asking 500$ USD

That’s under my budget but I am wondering if the dot will increase over time or not , if it will stay like this then i am ok with it as it’s not that much of a noticeable I am saving around 200+ if I go with this than a non repaired phone but I rather choose to save some money by going with it , my main concern is will the dot increase? , will it cause any trouble? , thanks for any advice