When looking to rent a condo/apartment, a condo owner admitted, that the advertised "living area" includes the parking space.

I already had the suspicion several times that the way of calculation here is highly flexible.

For example, I see a condo, advertised as 102m2, and it looks like a floor space of 80m2 to me.

I measured the places I have stayed so far and with a lot of good will, including balconies, I get around 10% less floor space than the advertised area.

I may have been just unlucky - but what is your experience? Are balcony areas part of the "living area" and what else is added to the pure floor space of the condo?

Thai floor areas are solely a product of their imagine only and really have litttle to do with actual living areas. Of course the real usable area should be based on internal floor sizes but you will find in Thailand it is generally measured using an elasticated tape externally. Of course if you look at a house area you will find they consider the area used for car parking is also part of the livable area. Best to check and measure yourself which of course doesn't help you when looking at adverts but a good rule of thumb for real usable area is assume 75% of what is advertised.

The area is the amount of space that is yours and not usable by other, not common area. If you have a private car parking space then that is included in the area. Along with any private balconies, small bits entering your unit, even the thickness of the walls and the services shaft as it goes past your unit.