Hello,
my name is have2brothers.  I will take you through the steps of buying Pokemon cards the smart way.

1)Buy cards in bulk.  When you buy cards in bulk, it is always cheaper.  One reason for this is that you only have to pay shipping once.  Say you want a  Charizard and a Blastoise.  If you buy them for $5 each and pay $3 shipping for each of them, the total would be $16.  But, if you bought them together for $10, you would still only have to pay $3 for shipping (people don't raise shipping prices per card when selling in bulk).  So, the total would be $13.  The $3 you save by doing this adds up every time you do it.  Say 60 holographics are selling in an auction.  This auction might sell for $60 including shipping.  This means each card was purchased for $1.  If you bought each one of these holographics seperately, shipping alone for each one would be over a dollar.  Buy cards in bulk and save.

2)Don't buy auctions that don't have pictures.  Say an auction title is Holographic Charizard.Very Rare! and the auction had no pictures.  There are at least three holographic Charizards that have promo written on them, and are therefor classified as fake and worthless.  If the person gave a description of the card like this: Holographic Charizard.  Very Rare!  120hp with 100 attack, you still couldn't be sure.  I have a Charizard that is holographic, has 120hp, and has an attack that does 100 damage.  It also says promo on it.  Auctions that don't have pictures are no good unless the name of the attack and number in lower right hand corner of the card are told too.  Promos don't have a number in the lower right hand corner.

3)Don't buy expensive cards if they don't come with a protective sleeve.  Any holographic card (or just a card purchased for over $1) should come with a protective sleeve.  Say you buy a Lugia ex (easily the most expensive single card sold on eBay) for $30, which would be relatively cheap for the card.  Nowhere in the auction a protective sleeve is mentioned.  If while being shipped, the envelope the card was placed in gets bent, you can not get a refund (unless you purchased insurance).  Paying $30 for a card in perfect condition then receiving it bent due to a shipping mistake is not a joyful experience.  Never purchase cards that are not sent in protective sleeves.

4)Make sure the quantity of what your buying is clearly stated.  Say there is an auction selling 900 Pokemon cards.  The description tells you that there are many holographic cards.  The adjective many is an opinion an could merely mean there are ten holographics in the set.  If you purchased the set hoping for twenty or thirty holographics and you only received ten, you couldn't get a refund because a specific number was not given.  One case in which it would be okay to buy an auction in which the exact number is not given is if the description said 100+ holos or 30+ holos.  In these cases, you know at least how many cards you would receive, and can now how much you would want to spend.  Remember, make sure the quantity of the sale is told.