Yeah, we have been getting a few of the newer Kindle Fire in for charger port issues and that's very easy but I don't normally promote it. Just thinking about any other things to add to the list of crap we do to bring in a little more money.
If you want to get the most bang for your buck so to speak, I would stick with very common and or easy devices. If it were not for having other techs who specialize in mobile device repair, I would not touch them. Each of them are different and require a specific skill set that you really can only develop from repairing tons of different types of phones and other mobile devices. Point being, unless you are getting a lot of them in and unless you got someone who can dedicate their time towards becoming really good at repairing them, you are going to dump a lot of time and money into training yourself to do repairs that are not very profitable. iPhones, iPods, iPads and Galaxy's on the other hands are so common and or simple that you will quickly become proficient at those repairs and make a decent profit. Charging port replacements are also very simple on the Kindles, just keep in mind that if you obviously get a lot of Kindles that are not worth repairing as well, as with any other repair obviously.
If you do want to do more Android Phones, than I would suggest only repairing those that you can get the full screen and frame assembly for. It will make your job 10x easier. Personally, we decided that it was not worth our time repairing Android Phones unless we could get the full screen and frame assemblies, so if we look up the part and it is not available, we don't fix it unless we know it is relatively easy. For us, it is just a matter of sticking with what is profitable and not wasting our time on anything that is not.
Color changes for the iPhones is another thing I would suggest looking into. If a customer already has to get their iPhone repaired, they are often times willing to pay a little more for a different color.
Cases for iPhones, iPads and Galaxy's are another thing you can make a decent profit on.
We also sell screen protectors that we buy in bulk. Two iPhone front screen protectors for $10, one installed and one extra. This does not seem like a lot, but if you get 10 phones a day in and get 5 to pay for screen protectors, it adds up.
You will also want to pickup some g-tools from WGP for iPhones and iPads. The will make your life a lot easier when it comes to bending back the housing. Also, we charge a little more for this service, which allows us to be cheaper than the competition. Competition charges $135 for iPhone 5 screen replacement, we charge $125 as long as the housing is in good shape. If it is not, then we charge $25 more. It allows us to make more on the more troublesome phones (and to pay for the tools), while still being cheaper then the competition.
Anyways, those are just a few ideas off the top of my head.