Question

How did the Arab merchants try to keep the Portuguese out of India?

Answer 1

Arab merchants told the King the portuguese were thieves and that no ships should be visiting anymore

Answer 2

There were many ways varying from plain sabotage where they claimed that the Portuguese merchants were thieves, up to more controversial means such as ordering their assassinations and telling the king that he should have them killed because they didn't give him presents and plan to enrich their wealth at his expense.