RE: How to use Pokemon Shopping sites, and where to go.
You may want to add Dave and Adam's Card World to the list. I hear they're an excellent place to get reasonably priced boxes (and often have a whole bunch of different ones in stock) but from personal experience I would not recommend buying singles from them. Everything is listed as Mint, but I ordered some cards that were clearly not Mint, under standard T&T quality (edgewear, lots of scratches, one with a little crease) and they refused to accept the return, claiming that the cards I returned were not the cards they sent me even though I had literally done nothing except remove them from the toploaders, examine them, and put them back and return them. Poor customer service, and I expect that I'll have to file a claim with my credit card company. Shipping is also expensive.
On the other hand, I have always had good experiences with Professor Oak. When he says Mint, he means it - the absolute worst that I have gotten from him is a few minor holofoil scratches, and his level of customer service is unparalleled. He is also a one-man business, which is pretty incredible considering how much he has in stock and how quickly he responds to questions. Prices are high, naturally, but quality matches the price. If you wait until his dynamic prices fall to 60% of the full price, which happens naturally over time, you can get some great deals.
T&T's quality is subpar, I have received some cards with minor creases and tons with edgewear and a lot of scratches, especially with collectibles. Put it this way - if you bought T&T's cards and tried to sell them to Professor Oak, he would not accept the majority of them. However, T&T does have solid customer service, although it may take a few days before they respond. I expect that from a company of their size, though. They ~used~ to have good prices on some collectibles, but over the past few months the prices have skyrocketed. Many collectibles that were much cheaper at T&T than Professor Oak in the past summer are actually cheaper at Oak now, and you'll get better quality to boot. 99 cent shipping for up to 99 cards is a great deal.