A general rule of thumb is preview the price of given card at Starcitygames, multiply by 2. The end result is what x4 of the same card on ebay will in general go for. I'd compare Ebay to the stock market, prices ebbs and flow depending on the current type2 (and as of late) type 1 metagame. Usually the big sellers (Starcity, Troll&Toad) are about one to two days behind Ebay. So if your observant you can snatch some deals right under their noses (as I did with Solemn Simulacrum). Some argue there's a degree of risk when using Ebay's service and with that I'd agree with one caveat. For many selling on Ebay is their chief income. You don't reach a feedback rating of over 1000 by casually posting a few cards here and there...remember not everyone supplies feedback either positive or negative upon receipt and to reach this level your doing serious buisness daily. I'd argue that for some Sellers (with over 600 feedbacks) your taking the same risk in purchase as you are with the traditional internet retailers (Will they ship promptly, will they use my correct address *Troll and Toad couldn't do this with a purchase of over 700 dollars..needless to say I'm done with them*, will they pack it well).