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Jeroen, an used Argentine registered bike can be sold, or purchased in Argentina by a foreign tourist, only if the the owner, (the person to whom the vehicle/moto is registered) is present. The owner listed on the title must be present, present documentation, provide verification that all yearly taxes have been paid and a certification that the bike has not been reported stolen.
I would like to share what I know, but need more info from you, before I can answer your question.
Here are some general guidelines.
If you do identify an Argentine registered bike in Peru it would have entered Peru under the rules and regulations of a Temporary Vehicle Import Permit, issued to the owner at the border when the bike entered Peru.
In Peru, as in most South American countries it is clear that it is illegal to sell or buy vehicles/motorcycles that have been issued a Temporary Vehicle Import Permits, until the vehicle/moto is officially registered in the country that has issued the Temporary Vehicle Import Permit. The majority of South American countries levy a steep import tax on foreign registered vehicles/motorcycles before the title can be transferred from the country where the vehicle/moto is registered to the country that has issued the Temporary Import Permit.
Generally speaking, only citizens of the country or official permanent foreign residents can have a foreign registered vehicle/moto that entered on a Temporary Vehicle Import Permit (TVIP) registered in the country that issued the TVIP. The title transfer process is a lengthy procedure and the import tax is calculated well over half the determined value of the vehicle/moto.
So it would be impossible for you, who might be a foreign tourist in Peru, to buy or sell a foreign registered bike that has entered Peru on a TVIP.
On the other hand you as a foreign tourist could legally buy a new or used motorcycle in Argentina, tour Argentina and then legally sell your Argentine registered bike in Argentina, no problem.
What you might not be able to do is leave Argentina with the bike. Like Chile, Argentina imposes strict export regulations on foreign tourists who have legally purchased motorcycles in Argentina.
I do not know if there are similar restrictions on foreign tourists exporting their legally purchased Peruvian registered motorcycle. For that matter, you would need to consult with someone else.
I need more details of your plan, before I can comment on your specific situation. Hope this helps
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