Soundtrack's method is quite unstable, but yeah, while you're waiting for your opponent to move, it's a good idea to just keep refereshing the market, sorted by date (don't refresh the page, just click "By Date" to refresh) and you may either get a card from someone who made a typo, or from some desperate guy who is consciously selling a card for few thousand less, just to sell it quickly. Keep the 5% tax in mind though. When the price is around 20,000, buying it for 19,000 brings you no profit. That is, unless you actually want to play with the card
On the left hand side, you can click on your name - it will take to your page. Right above your "Level", "Rank" and "Stars", there is "Click here to change your account details and preferences." button. There you can click on the "Your preferences" tab. Look under "Market". Under "In the Market list of deals, I would like to see" you can chose either "Trends" (shows if price have been rising, lowering or the same and what those prices are) or "Graphics" (Basically shows the sales history). Now you can combine this with "My default graphics for the Market" that sets the time period of the previous option to either "Day", "Week", "Month" or "Year". This will give you pretty good idea what the prices are like. But please, don't become one of those maniacally refreshing market-sharks. Those brothers don't have life and play time.
Prices fluctuate it all comes down 2 the card you want if it's rare card at a cheap price buy it asap chance is it's gonna go up, also it doesn't hurt to wait a rare card that is expensive will likely decrease to a more affordable price jus dont wait too long and last developing cards that are rare or uncommon are the best to sell at a high price for example my lvl 3 peeler could be sold for 15000 i never even thought it's price would raise but it did keep a sharp eye open get em while their cheap thats all the expertise i can offer the rest it up 2 u gud luck
Some cards in New Blood may have a very low price due to saturation of them via New Blood packs. Buy them before they leave New Blood (a few weeks after their release of course), then sell them after a few weeks - months.
For example, way back in the day I bought Wardom at 3,000 Clintz and 70 Krashes at 150 Clintz. Wardom now sells for a whopping 10,000 Clintz and Krash for 300-400 Clintz. Yes, it took a long time, but getting the Big 5 just from buying them takes a long long time.