The guide you mentioned is a good reference, but you must always cross check with Public trades in game knowing that, most people lowball to get the card, and "alley oop" when trying to sell. You'll see a lot of those one over the other, same person offering 2 packs for a card, and next trade, same person wanting 4 packs offering that same card. At the end, this would mean a fair value of the card is at 3 which wouldn't be paying the high value, but either lowball no one. Although you can try that 2 packs to start, or 2'33, 2'5, 2'75... with two 1 value pack and one older one valued 0'5 or whatever.
In addition, a lot of the referenced values in the guide are high itself. Other are ridiculously outdated. But at the end it's something to get kind of reference and a ton of people use it. It's useful but values are not even close to be set in stone.
Market itself moves. A card today is 2 packs can be 7 "tomorrow". Of course is not that fast and variations use to happen slow, This movements come together with the IRL tournaments played worldwide. If a deck does TOP8 and includes something that was not played since then, that cards will rise price. Maximum example of this is when new sets are released (next is February). New cards can make some older ones not played, become strong. A reinforce of Dark type or Grass type in GX or trainers form, can make new decks so non used cards since then become relevant to the format and rise price. Good is to have a complete playset of everything before the new release. At the beginning prices are crazy, then tend to go down and stand long term, decreasing little by little.
RA means Regular art, FA means Full art, RR means Rainbow Rare, SR means Secret rare. And the rarer, higher the price.
About opening packs, the smart is never open unlocked packs. But it's so funny. However, you must open every locked pack you get (what else can you do with'em if not?) and soon or later, you'll be able to release an unlocked copy you own of a card because you got a locked one. Opening is always up to each one but nothing guarantees any good card or card you're looking for, opening packs. Make the test with locked packs and long term you'll see the results are poor.
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5th day reward packs list http://forums.pokemontcg.com/topic/56679-5th-day-log-in-pack-is-random-got-a-gur-dd/?p=593037
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