If during a taxi journey the driver asks you to go to a shop so he can have a docket stamped so he gets a free tire/service etc, be firm and say no. Otherwise you will spend the next couple of hours at a jewelery store or the like having the hard sell at inflated prices....
When bartering always be careful before the handshake as they have a tendancy to up the price slightly just as you are about to shake hands, dont know if they just do this as a joke as have never been caught by it.
Also after bartering if you have agreed a price then you will be expected to purchase the item, if you then walk away and dont buy the item you can expect some hassle (and so you should)
Dont buy anything for your first few days until you get an idea of what you should be paying etc, as you can get royally rip'd off. Remember a person paying 2000 rupees for a sarong
, we bought the same sarong from the same seller whilst the woman was still there for 150 rupees.
Also if you dont get the price that you want, dont worry just walk away, either the shop dude will come running after you and agree your price or you are in fact to low so at the next stall just up your price a little.
Dont listen to any sob storys about how they are making a loss or no money on an item so they can squeeze a few more rupees out of you after you have agreed a price, no shop/stall will sell anything if they are not making money on it.
Also remember that the products that you can buy are available everywhere so if you dont agree a price at one shop/stall/beach seller you can be sure the same item will be available elsewhere.
Lastly if you get a bargain great if you dont its nothing to worry about as another bargain is just round the corner.