The Dastaks were permits or passes issued by the Mughal authorities, including regional rulers like the Nizam of Bengal, allowing the East India Company to conduct duty-free trade. However, these Dastaks became a major source of conflict for several reasons:

Step 1: Understanding the Purpose of Dastaks
Dastaks were originally meant to allow the East India Company to import and export goods without paying customs duties, as a privilege to encourage trade.

Step 2: Misuse by the Company
The Company started misusing these Dastaks for internal trade within India, not just for import-export. This deprived the local rulers of revenue from taxes that would normally apply to such trade.

Step 3: Misuse by Company Servants
Employees (servants) of the Company also began using Dastaks for their private trade, further extending the misuse beyond the Company's official activities.

Step 4: Sale to Private Merchants
The Company and its servants even sold Dastaks to Indian and other private merchants, allowing them to also trade duty-free. This not only reduced government revenue but also created unfair competition for local traders who had to pay duties.

Final Answer: All these actions—misuse for internal trade, misuse by servants, and sale to private merchants—led to significant conflict with the Nizam and other authorities, as it undermined their economy and authority. Therefore, the correct reason is that all the above factors contributed to the conflict.