Usually, if you have a very inhomogeneous liquid-to-vapor ratio in adjacent fluid inclusions, they were a product of necking down. Boiling will produce two families of fluid inclusions: liquid-rich and vapor-rich. In any case, if you perform microthermetry on these fluid inclusions you can use the beahviour of data to decipher between necking and boiling.

I am very thankful for your answer but how inhomogeneity is the determiner? or its pertinent to some factors?

This is difficult to decide. The best way, if you don't have textural proofs of boiling (bladed calcite) i to start with a very accurate petrography, to classify the different typs of fluid inclusions as FIA's (fluid inclusion assemblages) in function of the position of the FI's (along growth zones, fractures), if they are primary, secondary, pseudosecondary... finally, to generate a map with the distribution of FI's and finally, to populate the map with Th's and Tmice (or salinities). With all this information, you can decide if boiling took place or not... you'll see if it make sense.

The underlying assumption seems to be that the fluid is water and the gas is water vapor. No CO2?

To J. Tritlla's reply, I add the suggestion that you measure T-decrepitation.

Yes, as you have just guessed.

it can be explained by unusual phase ratios in a nearby inclusion (e.g.too much halite and too little vapor).

However, boiling is likely to generate heterogeneous fluid inclusions entrapment (for example, one inclusion is %80 vapor or the other is %90 liquid).

Usually, necking down gets misinterpretations as heterogeneous entrapment, which is something else.

Bakker & Diamond, Am. Mineral., 2006