Are international happiness rankings reliable?

Not in the slightest; if they were, the measurement would be rather useless anyway. It's easy to skew the issue temporarily; typically this works for 5-10 years and then it comes crashing down. Greece did it come 2004 until their crash in 2009.

GDP per capita is the most reliable and closest measurement to a happiness measure.

Really?

So money buys happiness?

I'm not entirely convinced.

But I'm all ears. Tell me more if you have a moment.