By buying it outside your country you would need to follow their rules in terms of warranty; some retailers may offer international warranties, some may not, and you may thus end with no warranty at all.
As others also already stated, any additional tax applied in your country to such wares will have to be paid (if it wasn't in the country you bought it from).
Last, but not least, you may have to pay import taxes once you cross the borders, which are or aren't applied on per-region and per-category basis with different evaluations.
In the end, you'll end up paying the same you woukd pay in your country (or more). The only way you can pay less when importing is having an extremely favorable currency change rate (e.g. 1 unit of your currency is valued 3 times over a foreign currency).
Buying it from your country, when available, is almost always the best option.
Should you, however, buy it online, it depends on which service you use. Amazon does provide some grade of warranty if wares are sent directly by them from one of their warehouses, but in the end it's up to the shop it's sending the order to.
If Amazon has an Indian branch and you trust your country's shipping services, buy from there.
As a side note, keep in mind that, although the consoles and the games are region free (any game of any region works on any console from any region), DLCs are not. If you own an American game, you will need American DLCs downloaded from the American PS Store with an American account.
[off-topic] Wrote this quite fast, hope I didn't write any absurd thing or non-existent fact
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