My girlfriend's mom dropped the iPad a few years ago. So, last year, I bought an iPad that was locked, specifically, because I wanted to get the parts from it. I did try to contact the original owner, but never responded. He lives in Florida, apparently. So I parted with the battery, rear camera, headphone jack, speakers, the lcd, the digitizer, the casing, all the screws, the shield, the wifi cables, all the buttons, and the front camera.
Well, my gf's iPad had a broken top right part of the digitizer, but I was able to take it off with all the parts intact. However, I tried heating the iPad with her blowdrier, to take the digitizer out, and when I pushed it up from it's position on the casing, it broke. So, she is left with her original digitizer again. The good news is that, I replaced her entire casing without a hitch, and while doing so, I broke her little microphone that's under the front camera. The flex cable is extremely small, and you need a flat prying tool to really get it off without it breaking. I didn't have one, and when I tried replacing it with the other iPad's one, well, that one broke as well. So I bought one from ifixit.com, paid $40 total to get it shipped next day air, and placed it as soon as I got it. It works fine now, and my GF is happy again.
I recommend to buy the biggest tool set you can afford if you're repairing as a business, and if you're just repairing one time, get just the recommended tools on the guides and an ESD bracelet. And don't loose those screws, and follow the guides exactly, even when going backwards, so you don't end up with extra screws or screws in the wrong place. Also make sure the screws are in the right places. You can make a little diagram on a piece of paper, then just place the screws on top of the diagram, so you know where each one goes. Some are the same width, but might have different lengths, so a diagram helps you to finish the job a lot faster.