How is this a "guide"?
In any case, I will make a few comments about the market system and the "fair trade" concept. The game designers have arbitrarily set what they consider to be "fair trades" as a 2:1 ratio from one age to the next. Obviously, this ratio does not reflect the actual market value of these goods. Not only are some goods more valuable than others even in the same age, the ratio changes depending on the age especially, especially at the higher end.
As a player who has done a lot of trading, the InnoGames "fair trade" idea has caused me a lot of grief in the form of guilds sort of adopting the golden ratio blindly as a policy and making the rule that guild members can only post so-called "fair trades". I actually got forced out of the first big guild I joined because I posted a lot of "non-fair" trades on the open market. Note that none of these trades were posted on the guild trading threads, only on the open market, which theoretically was allowed by the guild rules. Nevertheless, a bunch of members complained about it, so the officers made an ultimatum: stop posting "unfair" trades on the open market or leave the guild. So I left. Several of the biggest complainers were members who were abusing the trading system and saw me as "competition", which was absurd because my trades hardly ever conflicted with theirs. They just didn't want another trader in the guild, especially one offering market value trades.
Making arbitrary rules about prices is never a good idea, either in real life, or in a game. Just to illustrate this, let's see how the guys who got me kicked out of my old guild would operate. What they would do is post 1:2 downtrades on the guild thread. For example, they would post 100 Silk for 200 Glass. This is a very abusive trade and would not do well on the open market, but it would get executed on the guild threads because the guild had a policy of helping members do "fair" trades. Then the player would transfer the glass to an alt on the same server. The alt would sell the glass at market prices, for example, 200 Glass for 150 Silk and make a big profit.
There is a psychological element to it. I remember when I was trying to stay in my old guild I went to one veteran member who had executed a lot of my so-called "unfair" trades, and asked him if he would support me. He said, "No, I think you should only make fair trades." I said, "You have been doing many trades with me though." He said, "Well, I just needed some stuff to do something." LOL I was helping the guy get critical stuff done by offering market liquidity in goods that he needed, and he still wanted me to stop. Well, he got his wish, I left and went to a different guild, so now none of the players except a couple of friends have access to those trades anymore. This was a big loss to them, because at one point I was putting up over 100 trades on the market every day, which is a huge amount of liquidity.