Relatives have said for years that the fish sauce in America (which mostly comes from Thailand) can't compare to the real stuff from Vietnam. Rampant counterfeiting of labels (3.5 crabs vs. 3 crabs vs shrimp vs pink labels vs. blue labels) meant careful scrutiny of every bottle to make sure we weren't buying crap from a fly by night operator. After eating in Saigon, I had to admit that the nuoc mam did taste better there, although not enough to haul it home with me.
So this may be of interest to cooks of Vietnamese food on this board: New May Wah Supermarket in the Richmond is selling bottles of nuoc mam nhi under the Red Boat label that are bottled in Vietnam. Only ingredients are salt and anchovies from Phu Quoc, which is apparently the place in Vietnam for anchovies. $4/bottle --two different strengths: 40 and 35. The smaller bottle is the 40, which is stronger and more intense. (I don't know why you would buy 35--just buy 40 and dilute it with water if it is too much for you.) Flavor is very good--smooth, round, intensely fishy with a slight sweetness. Is it worth the extra buck? I thought so, but your mileage may vary.
New May Wah
719 Clement St, San Francisco, CA