What are the things you should take care of when building a commercial product?

What are the things that should be taken care of when building a commercial product with Arduino?
I will be using the ATmega328P and the Arduino ecosystem for a commercial product. What things should I be careful in both hardware and software so that the resulting product will be of commercial grade?

Things I could think of are choosing properly rated capacitors, EMI filters, esd protection,fuses.

Thanks.

could you explain about your product so people can help you in detail

As you will be using software that was written by other people you will need to ensure that you comply with the licence under which the software was made available. Most of the Open Source licences allow the use of software in commercial products, but you need to check to confirm that.

You have not said whether your product's "commercial" value is in the hardware or the software. If the value is in the hardware you could consider making your program Open Source which should help with licence compliance.

You also need appropriate terms and conditions (or a licence) to protect yourself from unreasonable customers.

But the real requirement is to make a product that works as the customer expects and to provide appropriate after-sales service. For example can you quickly replace a product if one of them is faulty. Or can you answer customer questions if they have problems with software.

...R

Document things very carefully, using source code management tools for both hardware, software, documentation, and website. And preferably tools as well. Track bugs ,customer complaints, and idea for new features.
That way you at least have a chance of having newly hired programmers fix things while you company bigwigs jet around the country.

Decide what your company role, and your personal role is going to be. Best, cheapest, best supported, easiest to use, most continually updated, least frequently updated...

I think I would make a custom board with a stand alone processor , designed to fit a box and with decent connectors .
It would work out cheaper in the long run and probably more reliable.

You can then also include test points, etc to enable you to test completed boards or fault find .
Make sure all components work well within their ratings and document as others have said - you might need to supply hazard info, material data sheets and.... have liability insurance, pay tax etc .

further down the manufacturing stream, we used to send product accross the USA to california.
used each carrier and sent multiple packages.
then sent them back.
things like plug in wires would be un-plugged. things we never suspected would stop working.

but,
#1) use suppliers you know are dealing with manufactures. just because the chip has a printed label, does not mean it was made by that manufacture. even parts that cost a nickle are bootlegged.

#2) test every part of every circuit. scope out the signals, etc do the engineering correctly.

#3) read the data sheets. a guard ring costs nothing but can make things work correctly, or avoid problems from cheap PCB’s

on my first boards, I add in a lot of extra pads and if there is room some free breadboard area.
some times you need to add a jumper or resistor or capacitor and trying to add one to an existing device can be hard.
once you have worked out the bugs, then downsize, finalize the board.
bring all pins out to a pad. I have added sensors/inputs in round 2 and it is much easier to connect to a pad than a pin.