I think I"m doing this right, but thought I'd ask to double check. If you research a tech that provides a coin you don't benefit from it right away do you? As in I am at 4 coins, I research a tech to give me a 5th. I drop to 4 trade not 5, right?

I'd say correct since, as I see it, you pay for the research before you get the tech...

I'd interpret that differently. From pg. 21 "Example 2: If the player from example 1 possessed four coins, they would retain 4 trade after learning Sailing."

This is saying you first learn the tech, and then you retain trade based on the number of coins you possess. If a tech gives you a coin, I'd count it toward retaining trade immediately.

I suppose a rules question should be sent in to get an official answer.

Although I think that either way would work since it's not really that much of a game-breaking thing. As long as all players agree to going either way of course.

I think I'm wrong on this one. Having slept and looked at the rule book again, summarizing, it says players place the researched tech facedown in front of them in their pyramid until all players are ready to reveal their newly researched tech. In this regard, you'd have already spent and retained trade from coins, before the tech is revealed.

This is yet another nuance part of the rules my friends and I have played incorrectly; we'd research simultaneously but simply place the tech face up - in some cases, allowing others to see their opponents tech before choosing themselves.

We've always played it so that when you research a tech, you get the coin straight away and then you drop down to your new amount of coins. But I guess we could have been playing it wrong.

Well, I read the rules differently. I would say you actually get the benefit of the coins on the same turn you research. According to the rulebook:

"The only exception to this rule is for players who possess coins. Coins allow a player to retain 1 trade after researching for each coin the player possesses."

The key here is that you retain 1 trade AFTER researching. And later in the rulebook is this:

"So, for example, when a player learns Engineering, which unlocks Aqueducts, they flip over any Granaries they’ve already produced, immediately upgrading them to Aqueducts."

The key in this sentence is that you IMMEDIATELY upgrade your buildings. So, that goes to follow that you IMMEDIATELY gain a coin from a tech. Seems clear to me that if you were at 4 coins and learned a tech that gave you a coin, you would reduce your tech down to 5 coins.

It sounds like the Board Game could use an Official FFG FAQ Sheet clarifying the rules...