Oh, hai Doug! I would say Ebay is the most fair pricing method for reporting gains and losses because you can actually buy and sell at those prices multiple times. The more heaving sold a card is, the more reliable the pricing is. MOTL is pretty good at this, but there are a few issues with it. One, their price guides aren't updated every day. I don't know what it is, but I think it's like once a week or something. Trends can happen pretty fast. 2, and this is against Ebay too, is that it's unreliable on cards that are not sold or traded often. For example, I looked up an Ice Age rare, Formation, and MOTL listed it as $1. The card is obviosly complete trash and only valueable to ppl looking to complete a set, and Ice Age isn't hard to come by like Arabian Nights and to a lesser extent Legends. It was listed at $1 because only 1 auction happened, and someone actually paid a dollar for it for some reason. Naturally, I didn't ask for that card to be valued at a dollar.

TL;DR:
As long as the card is traded or sold with at least a little frequency, I think Ebay and MOTL are the most fair ways to price your cards.

Also, your pricing system is crazy. While it seems balanced if you overvalue both sides, it doesn't always work out that way. If you view things as a percentage, you'll see why. Drowned Catacombs @ $5 is easly 100% increase. Verdant catacombs @ $11 is only a 10% increase. Most of the online stores overcharge more on the cheap stuff than the expensive stuff. For instance, many of their $1 – $3 rares are really only worth .50 on an open market like Ebay or MOTL, making them 100% overpriced, but Vengevines for $40 is only 12.5% overprice if they actually go for $35. The most fair pricing is Ebay since that is what you can buy and sell them for anytime you want. If some of the websites end up making a mistake, you can make some $ by arbitration, but Ebay is the most accurate pricing system for showing gains and losses because that's usually the best price you can cash out at.

If you want to write something valuable, show us how you are getting people to agreeing to those trades. Show us your methods and reasoning behind them. Tell us why you chose a particular card of theirs to trade for instead of the others you had to choose from.

One last thing. One of the factors SCG base their pricing on is how many copies of the card they have in stock. I've seen them sell out of a card at one price and raise the price of the card while it's sold out. That is probably what they did with Wurmcoil Engine. That's also what they did with Mox Opal at one point.

For high-turnover cards, do you suggest we implement MOTL pricing on this site as a standard? I'd like to hear back from you guys on what sites you use to accurately price your cards.

Wurmcoil Engine is not 20, its 13.
Kozilek is 7.
Fauna Shaman is 7.

I don't give a crap if SCG is paying your bills. This is misinformation, and you're nickel and diming yourself. It's so bad that I would have happily been on the other end of almost all your trades.

This is why I let other people use SCG when I'm trading up. They're shooting themselves in the foot and I'm profiting from that. However, you guys are supposed to be the authority on trading, and you're falling for beginner crap like this.

The best way to value a card is "what would I have to pay to get this card by next week?" That means the minimum price from a store. Not the mid or the high (SCG).