Many travel sites have reported the problem and the frustration that nothing being done about it. From TripAdvisor article excerpt, see article at
http://www.tripadvisor.com/Tra...

A Guide To Proper Taxi Companies

1) "A-list" companies that use an uniform car park and rent exclusive taxi spot slots. They are more expensive, but the chances of being cheated by them is also minimal.


Tulika Takso (+372) 1200 2.88 + 0.55/km (0.70/km)

Tallink Takso (+372) 1921 3.20 + 0.77/km (0.88/km)

Tallinna Taksopark aka Tallinna Takso (+372) 6555555 or (+372) 1555
3.60 + 0.69/km (0.88/km)

Taxi fares in Tallinn are unregulated, beyond the stipulation that they must be posted on the rear passenger-side window.
The average tourist is hardly inclined to go, from cab to cab, comparing rates; so, free-market competition hasn't evened them out.
I've learned to avoid the yellow cabs: they're the most expensive.
The white ones offer a good rate.
I can't comment on the others, but; hotel clerks are generally a good source for advice.

Why doesn't our self-proclaimed expert on Estonia, the mouthy Maxim de la Trine, ever offer us any useful info?