Coming from abroad: How many items can you bring?

Me and one of my friends are travelling abroad from India for the next 3 months. A lot of people in our circle are requesting macbooks. iphones and DSLRs to be bought from there since it’s usually cheaper there.

I have been reading a lot of customs rules, and they seem to be highly strict for these, but nothing explicitly is mentioned about unboxed items.

I wanted to know about these cases from people who have experienced it before. If I unbox and use the items, will they be allowed without duty, and will I even need to declare them?