Cannot speak on Pi 3's, but I know some troubles existed on older Pi's. See http://goughlui.com/2015/02/19/the-raspberry-pi-2-not-all-from-the-uk/ for some discussions by a member of element 14. Unless the costs are much different, why buy in China with longer shipping time generally. But some say no differences were found. Anyway caveat emptor.
The aliexpress suggests they are buying them from element14 or RS.
Warranty would be one consideration
Have you checked out the local element14/Farnell in your country.
I know they have a 'Business to Business' relationship meaning that they aren't meant to sell retail but for the nz site you select business use and it's fine.
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I would ask in Feedback and Support about purchasing in Saudi Arabia.
I do know there is an international site.
Whether this will deliver there is ??
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i would buy from aliexpress because amazon doesn't ship it to Saudi Arabia
I was wondering what is the difference between raspberry pi 3 model b on aliexpress.com vs on amazon.com
Here are the two links
Im planning to buy one and i want your opinion to make the decision