Reading back I think it may be a little confusing, I am not actually estimating, I remember a ballpark value, not the exact value. Not quite sure how it works :S. Possibly because I get prices from so many sources. Something just "looks" over- or underpriced to me before I even consciously think about it, though I may later remember what I last saw it at and where (or at what kind of place if not where exactly).

To be honest, I don't remember exact prices, but I can generally make a ballpark estimate. If a $25 card is listed at $20 I probably will not notice, if it's listed at $10-$15 I probably will. Foils give me a harder time than regular cards, but the same applies.

And yeah, lucky that way :D.

Pi, that is so true (and you are lucky to possess an astute memory). So much of finding bargains is keeping familiar with card prices. This is perhaps why I target online venues primarily to find underpriced deals – I simply can't remember all the values of foil EDH cards and random Legends cards. Shopping online means I can constantly research prices on various websites to confirm the deal is a good one.

EDH is a strange beast for people used to competitive. I am guessing most pricers at shops are used to that, just as most people here on the site. It's a very good idea to try to understand the mindset of the people who are fanatical about the EDH format. I have just 2 fans of foils in my group, but I can easily move at least half the underpriced foils I get to them and the rest I can move online.

I once did a very extensive aptitude test to find out what kind of career would suit me best. I turned out to be fairly good at everything with very similar scores on all different dimensions they scored on with a single exception. I got a much higher score on memory. In magic I always seem to surprise my group with knowing even the most random cards from memory, they used to read the card out loud when I asked them what it was, after me responding a few times with, "ah, it's a …" they now just name it. What I am trying to say is, as far as prices for obscure cards go, I'm really quite good. I will know not only if they have underpriced that Sword or other popular card, I will know if they have underpriced some random Legends rare most people haven't even heard of (say Invoke Prejudice or something similar). If you don't have the memory for it, it might be very difficult to make use of these situations when you're in a Brick and Mortar store and more time consuming when you're checking out an online shop.

Your comments on EDH foils is a great one. I know so little about EDH foils, so I cannot really elaborate. But there are so many obscure EDH cards worth money, it only makes sense that there are some huge opportunities there. Thanks for building on my article with those adds – great points!

While I don't follow ebay I do follow similar Dutch sites looking for good deals. Every now and then some underpriced collections or single cards pop up. I regularly make fairly low offers, knowing I likely won't get the item, but when I do it is very much worth it. Strangely recently some good deals even popped up on my own forums, 25 euros ($33.5) for a DCI foil sol ring, yes please!