I can't give tax advice in another country.
Under US tax law, bitcoin and other virtual currencies are treated as property, similar to collectibles, comic books, paintings, or other valuable physical objects. When you sell property, you have a gain if the selling price is more than the cost basis. For something you buy, the cost basis is what you paid. For something you receive as a gift, the cost basis is not the fair market value on the date of the gift, rather, the cost basis is the cost basis of the original owner/purchaser.
So under US tax law, if person A gives a gift to person B that person A paid $10,000 for, and person B sells it for $11,000, then person B has $1,000 of taxable income, no matter what the fair market value of the gift happened to be in the mean time.
Assuming the laws of country B are similar, that's why the scheme is problematic. Country B will view person B as not paying their correct income tax, and country A will view person A as being involved in a tax avoidance scheme.
The correct way to do this is some kind of agency agreement. If you sell a painting via Sothebys in London, you don't *give* them the painting, you retain ownership, they act as agent and collect a commission, which is their taxable income, and the rest is your taxable income. There are obviously ways to do currency arbitrage with "real" currencies where the trader pays the tax and the agent gets a commission, but I can't begin to tell you how to set that up.
