You need to have a real understanding of what the local currency is worth in your home currency. It's very easy to get blinded by large numbers.
I was in Indonesia, haggling over a set of wicker place mats. The exchange was about 9000 Rupiah to the USD. Starting price was 250,000 Rupiah for a set, about $27.00. We ended up paying 100,000, The price drops fast at first, and then we spent a lot of time in 10,000 R increments.
The funny thing is, that I wasted about 15 minutes per US dollar of savings. I could have quickly closed the deal at 160,000 or so, and moved on. We were blinded by the large numbers involved in the local currency. We saved 10000 of something, that's got to be a lot right?
Tips: If you are in a paternalisticpatriarchal society, and traveling as a couple, the act to put on is the eager, but financially naive wife, and the frugal husband. Let the wife do the bargaining. When bargaining gets a bit tough, then the angry husband should chastise the wife for wasting all of his money. This lets the shopkeeper know that there is a sale to be made, but the price will have to go down. There is a strong man around who is willing to put his foot down, and keep his wife from frittering away the family wealth.
This works well in southeast Asia, but not necessarily the Philippines. Filipino wives tend to rule the roost and the purse strings.