Gold for Gems and Gems for Gold

Gold for Gems and Gems for Gold

So I heard this theory today that you could watch the conversion rate, and say you buy gems in the morning and sell em for gold in the evening, like at the moment 1 gem = 3,6 silver, but in the 

morning it's around 2,9. Anyone thinks it's a viable tactic?

Doesn't work, take a look at the buy and sell prices - the buy price is higher than the sell price at any given point. Just like commodity prices in GW1, there's an artificial inflation (or deflation, from a selling point of view) of the price so you can't make money out of doing nothing but playing on regular price fluctuations.
No arbitrage, yo.
i.e. This weekend when I looked, buying 100 gems would cost you ~35s, selling 100 gems would earn you ~29s.
So... yeah... go for it if you want your money to disappear into magical gold-sink land a few silver at a time