user32463: I am thinking about making a real project using arduino to earn money.
What could be the objective reasons (from both a technical and a business perspective) to not use an Arduino in a real profitable project?

user4143: As a rule, no it's not a great idea.
Arduino boards are a prototyping platform. They are designed to make trying ideas out easy, not for permanent installation in a device. That's not to say you can't permanently install it in something of your own making, but when it comes to making a professional product it's not good, for a number of reasons:

An Arduino board is expensive compared to a plain MCU.
It's not a professional image.
It's not (typically) rugged and reliable enough.
Manufacturing something around a board like an Arduino is expensive.

The most professional way of using an Arduino would be to use something like an Arduino Mini and directly mount it on a custom PCB. But since you are making a custom PCB anyway, why would you incur the extra expense of an Arduino board when it is far cheaper to just build the required components directly into your board design? Also, when bulk manufacturing, you need to have as much of the build automated (i.e., surface mount to be populated by a pick-and-place machine) in order to keep costs down, and having to manually mount an Arduino onto a board adds extra expense (you have to pay a person to do the job themselves).

user30005: 
I want to know if there is anyone that has used Arduino boards in a real project? 

I have seen it being done, quite a few times.

What are the problems that you have faced?

Pros:

quick to market;
low cost accessories;
large code base to drop from;
...

Cons:

only workable for certain applications -> high cost per mcu (vs. bare chips), no possibility of passing certification of any rigor, no respect from others / clients, ...
quite inflexible an eco-system: porting code to / from others can be problematic.
poor project management capabilities.
...

Each of those pros / cons can be addressed and may not be relevant for your particular application.

32463: <p>I am thinking about making a real project using arduino to earn money.</p>

<p>What could be the objective reasons (from both a technical and a business perspective) to not use an Arduino in a real profitable project?</p>
 4143: <p>As a rule, no it's not a great idea.</p>

<p>Arduino boards are a prototyping platform. They are designed to make trying ideas out easy, not for permanent installation in a device. That's not to say you can't permanently install it in something of your own making, but when it comes to making a professional product it's not good, for a number of reasons:</p>

<ol>
<li>An Arduino board is expensive compared to a plain MCU.</li>
<li>It's not a professional image.</li>
<li>It's not (typically) rugged and reliable enough.</li>
<li>Manufacturing something around a board like an Arduino is expensive.</li>
</ol>

<p>The most professional way of using an Arduino would be to use something like an Arduino Mini and directly mount it on a custom PCB. But since you are making a custom PCB anyway, why would you incur the extra expense of an Arduino board when it is far cheaper to just build the required components directly into your board design? Also, when bulk manufacturing, you need to have as much of the build automated (i.e., surface mount to be populated by a pick-and-place machine) in order to keep costs down, and having to manually mount an Arduino onto a board adds extra expense (you have to pay a person to do the job themselves).</p>
 30005: <blockquote>
  <p>I want to know if there is anyone that has used Arduino boards in a real project? </p>
</blockquote>

<p>I have seen it being done, quite a few times.</p>

<blockquote>
  <p>What are the problems that you have faced?</p>
</blockquote>

<p>Pros:</p>

<ol>
<li><p>quick to market;</p></li>
<li><p>low cost accessories;</p></li>
<li><p>large code base to drop from;</p></li>
<li><p>...</p></li>
</ol>

<p>Cons:</p>

<ol>
<li><p>only workable for certain applications -> high cost per mcu (vs. bare chips), no possibility of passing certification of any rigor, no respect from others / clients, ...</p></li>
<li><p>quite inflexible an eco-system: porting code to / from others can be problematic.</p></li>
<li><p>poor project management capabilities.</p></li>
<li><p>...</p></li>
</ol>

<p>Each of those pros / cons can be addressed and may not be relevant for your particular application.</p>
