This is just flat out, 100% wrong. Mainly because "innocence" and "guilt" aren't even concepts that apply in civil cases.
All of your responses still seem to assume that businesses somehow have the same level of responsibilities and restrictions of a government, and that is just not true.
300 people in a 173 million people country do fraud, flag them all?
The truly genuine customers can contact the company directly and deal with them directly, rather than buying through a site.
When your per-capita GDP is a few dollars a day, the odds that the order for a multi-thousand-dollar consumer electronics item is genuine gets awfully close to zero.
You call it discrimination against an entire country, I call it a sensible policy for a seller to enact. If you'd like to volunteer to police these fraudulent purchases, I'm sure they'd appreciate the help, but when you have an entire department that spends most of its time dealing with orders from two countries, orders which almost always turn out to be fraud, the most sensible way forward becomes nearly self-evident.
As others have mentioned, you seem to draw no distinction between constraints on governments, justice systems, and private policy determined by individuals and companies. I think until you stop confusing the two concepts (and the vocabulary thereof), you'll have a difficult time persuading anyone to come around to your thinking. (To say nothing of forming a coherent ethical argument for why you think this is some great injustice and what possible solutions might be.)
If only 1% of 173 million had a western-like middle-class+ purchasing power, that gives you? 1.73 million. A lot of people you can do business with. Like 4x that of Luxembourg.
Presumption of innocence is even in the UN universal declaration of human rights.
What is considered burden of proof would be different, but it is still responsibility of the person forwarding the accusation. What you describe would be an accusation through "probable cause", described as reasonable grounds to conduct a search or investigation.
That being said I think country of origin are not reasonable grounds. Could be an individual sending money home, could be a merchant, could be anything.