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While in theory there may be some sort of a tax levied on a used projector, in practice nobody is going to care about it even if the customs inspector stops your friend. A single used projector is simply too low of a value for the inspection to bother.
If you want to be on the safe side, have your friend declare it. At the very most he will have to pay 5% of the value, which shouldn't be more than $50 for a used item.