Does som tam taste the same wherever you eat it?
No. The chilli and seasoning used and the way of adding sweetness differ. If the smell of fermentation is unfamiliar, it helps to ask first whether pla ra goes in.
Som Tam · ส้มตำ
If you want something crunchy and tangy, try som tam. It is a salad made by cutting unripe papaya into thin strips and pounding it with seasoning in a mortar. The papaya soaks up sourness and heat, and it goes well with sticky rice or grilled food. In Isan some versions use a fermented fish seasoning, so if the smell of fermentation is unfamiliar, ask which kind of som tam it is when you order.

Sour and spicy seasoning blends with the crunch of papaya. In the versions that use pla ra, a fermented fish seasoning, you can also notice the smell of fermentation. Even with the same som tam, the taste differs with how the seasoning and chilli are used.
If you want less heat, say so before it is made.
Som tam is a signature dish of Isan and is eaten in many Thai cities. Even within Isan, each area has different kinds, so you can compare the taste of som tam just as regional cooking differs across India. On a Khon Kaen trip, have it with sticky rice and other Isan dishes.
No. The chilli and seasoning used and the way of adding sweetness differ. If the smell of fermentation is unfamiliar, it helps to ask first whether pla ra goes in.
Not necessarily. Some kinds use fish seasoning or dried shrimp. If you are vegetarian, ask whether the seasoning and toppings other than papaya can be eaten.
If you want to read more about these dishes and regions, these sources are a good place to start. Ingredients and cooking methods can differ from one eatery to another.
Sharing image credit: Vyacheslav Argenberg · CC BY 4.0