Keep in mind that Indians will consider themselves gratified to go out of the way to fulfill a guest's request and will insist very strongly that it is no inconvenience to do so, even if it is not true. This means that there is a mutual commitment on you as a visitor to take extra care not to be a yoke.
It is habitual to set up a token friendly spat with your horde or any other member of the group when paying bills at restaurant or while making purchases. The etiquette for this is somewhat complicated.
In a business lunch or dinner, it is usually clear upfront who is supposed to pay, and there is no need to fight. But if you are someone's personal guest and they take you out to a restaurant, you should offer to pay anyway, and you should insist a lot. At times these fights get a little comic, with both sides trying to snatch the bill away from the other, all the time laughing politely. If you don't have experience in these things, chances are, you will lose the chance the first time, but in that case, make sure that you pay the next time. And try to make sure that there is a next time!. Unless the bill amount is very large do not offer to share it, and only as a second resort after they have refused to let you pay it all.
The same rule applies when you are making a purchase. If you are purchasing something for yourself, your hosts might still offer to pay for it if the amount is not very high, and sometimes, even if it is. In this situation, unless the amount is very low, you should never lose the fight. Even if by chance you lose the fight to pay the shopkeeper, it is customary to practically thrust (in a nice way, of course) the money into your host's hands.
These rules do not apply if the host has made it clear beforehand that it is his or her treat, especially for some specific occasion.
Any give or take of anything important should be done with the right hand only. This includes giving and taking of presents, and any transfer of a large amount of money.