When they go shopping in Vietnam or in other Third World countries, most Western tourists don't like to have to bargain. They think that each object has a price and that's the price every one should pay. It is neither logical nor fair that the price of an object should depend on who's doing the buying or on the bargaining skills of the buyer. And they are right, of course, in their rational Western way of thinking.
But if you look at it from the seller's point of view, it would be just as absurd, when dealing with a customer that won't bargain, not to ask for an inflated price, cause the sucker is willing to pay that price anyway, if not more.
My personal policy is: When in Rome... Of course, if you are visibly different from the rest of the population (i.e. if you have blond hair, blue eyes, red face, etc), it will be practically impossible for you to get to pay the same price as a local would. Even the Vietnamese living abroad (known in Vietnam as the «Viet Kieu») will get a different price rate from the locals, because we are supposed to be richer.
The point of bargaining however is not simply economical. It also has a social purpose: it is a mean of communication and a connection between buyer and seller. Sometimes, it is a struggle, to see who can outwit the opponent. Sometimes, if you're lucky, it can be a pleasant banter where you tease and get teased in a gentle, good-humored way. Some of my friends told me of nightmarish experiences where they ended up practically running away from vendors heaping insults on them. But all my bargaining experiences have been pleasant: like flirting without the sexual pressure. Usually however, the dialogue will enfold as follows:
Seller: Sir/Madam, please buy my doodads![Buy my stuff!]
Buyer: They look stale/wilted/past their expiration date. [Convince me. Why should I buy from you?]
Seller: Stale! I just cut them down myself this morning! Look, Sir/Madam, there's still some dew on them [I just sprayed some water on them]. They're only 10 dinars a kilo, but since you're my first customer, I can let you have them for 8 dinars. [All right, you're not as dumb as you look, so I'll just give you a token discount to get the ball rolling]
Buyer: I don't know. Are they sweet? [They do look good, but I'm not just going to take the first discount you give. Talk me into it]
Seller: Sweet as sugar, Sir/Madam [What did you expect me to say?]. Here, try one [I'm throwing you a bone here. Buy now!].
Buyer: They're okay, I guess. [I'm a sucker for freebies. But I still have some fight left in me]. How about 3 dinars a kilo?
Seller: Version A: You know what, you're obviously a connoisseur. I'll let you have them for 5 dinars a kilo if you take 2 kilos. [I'll still make money from you].
Buyer: [tired but satisfied] Oh, all right, give me 2 kilos then. [I can't spend more time and effort on this]
Seller: Version B: I'm sorry, Sir/Madam. These are of a superior quality. If you want cheaper ones, I think they have them at 4 dinars a kilo at the other end of the market. I cannot sell mine for less than 6 dinars and you have to take 2 kilos. [You're a cheap loser and I get to insult you while pretending to care]
Buyer: [humiliated but too afraid to just walk away] Oh, all right, give me 2 kilos then. [I can't spend more time and effort on this].
The seller is happy, the buyer is ill at ease and senses that he/she has been bested.