The connector doesn´t look well. I think one pin is broken. It is possible to replace only the connector instead of the whole motherboard. But it is very hard to say if there aren´t other broken components on the logic board caused by the water. I think you better bring this phone to an expert he will tell you if it´s worth to repair the phone or better to buy a new one.
You can test which camera is not working by using other Apps to start facetime cam. The app crashes and shows black even if only one cam is not working. But I guess it´s only the one on the back. Try this first because it's quite easier to replace than the front cam. If you still got camera issues replace the Facetime cam. This should solve your Problem. These guides will help you to perform the repair. iPad 4 Wi-Fi Rear Facing Camera Replacement iPad 4 Wi-Fi Front Facing Camera Replacement You´re quite lucky that you own the wifi version, which makes the replacement quite easier than iPad with cellular. And don´t use any sharp or metal tools when removing the touch screen this will damage the color coating.
Your only chance, in my opinion, is to use 3tools. You can try force boot maybe it boot to springboard or 3tools has a recovery mode where you can restore the device but keep user data. This tool is totally free instead of this other snake oil software on the internet. This is the official Homepage. 3u.com. If your device is still unable to boot there is one last opinion left. This youtube video shows you how to. This worked for me very often. You read the data directly from the nand chipset. https://www.youtube.com/watch?v=58-7cg9cYNY Good luck to you. I hope you have success.
I think it is the rear camera. A bad causing under voltage would cause more trouble like a unresponding or ghosting touch screen. Replace the rear camera first. This was a very common problem of iPhone 5 that the rear or front camera stops working and causes crashes of the camera application. If this doesn´t work out please post your results so we can check the next steps. Use this guide iPhone 5 后置摄像头更换 and good look to you.
First of all, Alibaba is no manufacturer it´s just a platform like eBay, especially for B2B costumers. If you mean aliexpress.com this is actually no good source for good quality. You should always buy in bulk because the reduces the price. It´s quite hard to find a reliable supplier overseas. There are many manufacturers that claim to have the best quality on the market, but who wouldn´t? You will need to do many test orders from different suppliers and you need devices to test the displays to really measure the quality. Check brightness, yellowing and so on...... It looks to me like you are just starting your business. So I would recommend looking for local or national supplier first. Or even use ifixit B2B. They offer really high quality and good prices and more important lifetime warranty. The most suppliers overseas only a 3-month warranty or better if you order very big quantities up to 5000 units. On top of that, it´s important to give your supplier feedback what should be improved to raise the...
You need to disassemble the total phone. You can´t lay the complete phone in isopropanol. This will definitely kill the speakers and both cameras (residual on sensor). Only clean the logic board. If there are any errors caused by flex cable parts, replace them do not clean them this won´t work for long therm.
Yes, it can touch on it´s own (called ghosting). There 3 possibilities that could cause your problem. 1. broken Connector ( measure connections between connector and) logicboard) 2. Broken Touch IC/Broken solder points (replace the touch IC on the logicboard) 3. defective or low-quality Display (test the Display you installed on your customer's phone on a phone with working touch and test if the ghosting continues But all in all this problem can be hard to fix because the phone was thrown. This hard acceleration can cause many defects on the logicboard, for example, defective solder pads or points or small cracks in the connection lines (which can cause temporary defects depending on the temperature of the logicboard)
The touch id button is connected over the 3d touch cable to the logicboard. This cable is very thin and fragile. You need to check this cable. It´s behind the metal backplate. You check out this iPhone 7 home button not working after screen replacement Check my comment and you will see what I mean. To repair this you need to replace the 3D Touch.