Shuttle XC60J is cheap industrial mini PC that that is aimed for those who want a low powered, efficient fanless computer. It has TDP of mere 10 watts which has allowed its manufacture to make it fanless since there is so less heat dissipation. Shuttle XC60J specifications include Intel Celeron J3355 processor, two SoDIMM RAM slots, three storage slots, Intel i211 gigabit Ethernet base and three RS232 ports.
Shuttle XC60J also comes with two audio jacks for the microphone input and the headphone output; Two USB 3.0 ports and two other USB 2.0 ports. Clearly, there is no shortage of ports on this mini PC. There is 65 watt power supply and the mini PC can be mounted using standard VESA mount.
It is guaranteed for normal operation 24 hours a day and 7 days a week if you have good air circulation around the mini PC.
Clearly, there are way too many ports for a normal user but nobody will complain for the extra ports on such a tiny machine. Keep in mind that since you will be selling it barebones, you will have to add your own RAM and storage. You can add upto 16GB RAM in it and three hard disks or SSD drives. There is no Wi-Fi onboard but you can add it via USB or M.2 2230 port.
You will also have to install operating system yourself. This is both good thing and bad thing. If you are going to install an open source operating system, you will save money as they do not cost money. One example of such OS is Linux Mint which is downloadable for free. Another example is Ubuntu. Read Ubuntu Remix review here. However, if you are going to install windows on it, you will have to shell out and buy a license as it is not free.