Reply #5? That's what I thought I was responding to already. OldTrees explained why having two ways to buy cards (a trading system and the bazaar) wouldn't work -- so I suggested modifying the bazaar (by having it adjust prices based on demand), rather than adding a second system.
(Yellow text shows my interpretation)
Trading for Common cards:
Either it costs less, the same or more than the bazaar.
Less: You can make Infinite 
by repeatedly trading X electrum for a card the bazaar will pay Y electrum for, where X<Y
Same: Waste of Code since you can trade with the bazaar
More: Waste of since the bazaar sells the card for less
...which is why I'm suggesting a
modification of the bazaar, rather than an alternative. Zanz has adjusted card prices before, on both a large scale (changing the rank of a card) and a small scale (changing the quantum cost of the card). For example, a rank-3 card with a quantum cost of 2 can be bought for 56 and sold for 38; changing it to rank 2, cost 2 would reduce these prices to 26 buy/18 sell, while making it rank 3, cost 4 would increase them to 58 buy/40 sell.
I'm saying that the bazaar should periodically load card acquisition and sale statistics from a database (possibly the same database that collects the card usage statistics), which it would use to adjust the price of each card (and then reset that part of the database, so that it doesn't make the same changes again unless similar deficits and surpluses occur at the new prices.) The "buy at the trading post, sell at the bazaar" loophole doesn't exist if the bazaar
is the trading post.
Trading for Rare cards: [Rare cards exist for a reason.]
If Nymphs can be traded for then they would not be rare due to the oracle spin.
If Weapons can be traded for then they would not be rare due to the 500 score reward.
Arctic Squid, Pharaoh, Miracle and Shards would still be scarce but much less rare even considering the Farms in T50 that currently exist.
I'm not saying there should be any new way to acquire rares -- in fact, my previous post even says my idea "wouldn't make nymphs grindable." Actually, it would probably make rares even rarer -- a high number of copies of a rare being acquired (and not sold) would lead to a higher sell price for that rare, which would lead to more copies being sold. (Exception: Relics would become more common, as not everyone would sell them immediately. Those who waited until Relics were more common would get more electrum for their Relic.)
Conclusion: Trading either is exploitable in a terrible way or is useless.
The only exploit I can see is creating many alt accounts with cards you want to sell on your main account, so that the main can get more electrum from selling those cards -- but I think this could be deterred by not gathering stats from low-score players. At the moment an account crossed the score threshold (100?), all the cards in that account would be considered to have just been acquired. (It would still be possible, but not as efficient -- and nobody will do it if it's less efficient than simply grinding on the main account!)
[Exception: An almost worthless version of trading would only accept Arctic Squid, Pharaoh, Miracle and Shards and cost dearly to buy. But if that was beneficial to the game then those cards could be added at that price to the bazaar.]
If making them buyable would be beneficial, then it can be done. The prices are already listed in the trainer: Squid and Pharaoh are rank 8, so they cost 384
(and sell for 256) plus their quantum cost; Miracle is rank 6 with a cost of 15 quanta, so it costs 231 (and sells for 159); and (unupped) shards are rank 1 with a cost of 1 quantum, so they cost 7 (and sell for 5). Under my system, if they stayed at these prices, it would be because the players thought they were worth that much -- or at least, worth somewhere between the buy and sell prices.
